Too tired to do much explaining. I'll state that in a perfect world my ideas would've been fantastic. The things I said I'd do were outrageous fantasy. I got up at 4:00 am on the 19th and pulled it all outside, set up main frame level, then put every piece of bed frame on main frame, went on to dove and that's where the illusion became apparent. With bed frame sides positioned perfectly with miters at front nothing with dove would line up, I had the bedframe done at 5:30 am and the dove took 4 hours. I got it after quite a bit of WTF... I started welding at 10:00 am and well... I'm a peculiar person I suppose some may say. I couldn't just weld without continually checking every piece for movement, oh the horror of imperfection is simply intolerable. I worked all day and until 1:00 am the 20th. Things have been pretty much a blur since then, I've worked on it one way or another since. I had an outside job scheduled with my work that had to be done so that drove me nuts. I'll update in more detail when I catch a mood. There is no end to what's enough. I ruined my press bed shaping the boarding handles (They had to be identical...) the boarding steps took a whopping 2 hours, couldn't have shin busters on MY trailer...I installed the lights I had today, also what WAS the plan, things change... I'm ordering more mini L.E.D.s right after this, and flood work lights, contemplating bed surface lights, either out of any conceivable way or dead center, flush without question... I put 3 per side under bed facing down on outside of wheels (tire issues resolved with glance in mirror) and it's evident 1 or 2 lights inside wheels would be logical... At any rate, here's the images... enjoy!

All about the Prep!

Working on getting lights set up. Here's the plan... Thursday morning early I'll get all bed frame channel on mainframe and pull outside, not sure if its been mentioned, but trailer almost 8 1/2 feet wide will not go through my shop door, once bedframe welded no more inside at my current shop. I'm thinking about looking for a larger shop because I'm getting calls to fabricate/weld on large equipment, dump beds, big truck trailers etc and I enjoy this type of work, as well, it's good exercise... I'm not capable of laying around... So, Thursday morning I pull it all outside and set up/weld all bed frame, then weld on stake pockets, install lights and go to steel company to pick up diamond plate. No mystery here if anyone's wondering, I've already explained I need one sheet cut lengthwise 32/16 (to avoid mating over short crossmembers at wheels) and that I need each sheet laid in its respective position on bed frame, we can do it with their crane/trolly hoist.
No time to play, I'll strap for security in freshly welded stake pockets, get back to shop, set up plasma cutter and remove triangle corners for boarding steps, weld sheet steel top and bottom (stitch) and then have a couple of my guys get on the primer, while I knock off weld slag and such with angle grinder. Then I can set up boarding steps and weld. I may have left out that in using these marine coatings they require you to "strike" coat all welds/joints first, then go over all. By the time they get close to being finished I'll start one guy back on paint. I'm concerned with bottom, time consuming...
I decided (diamond plate gets slippery when wet) to add a special step into the top bed coat as follows: I'm going to get them started on top of bed together and as soon as they roll out one 4X8 section, I'll sprinkle clean/dry sand on wet paint (I'm making a sort of sand shaker with a folgers canister, drilled holes in lid...) Then after that paint can be topcoated...Sand should be well into coating and sealed.
Weather permitting, that is the plan...
This evening I cut 3/4 inch holes in side bed frame channel for markers. Had to countersink (1 inch) holes in order to use mini L.E.D.'s (channel too thick) Annular cutters, mag drill... Here are images of that process, single hole. I drilled/countersunk 6. Last image shows light lit with battery...

Okay people or lack of them...Maybe I should just type Okay record... Heh. Sherwin Williams, understanding the nature of me and my extremely high opinion of quality and longevity, sold me an industrial primer...
Kem Kromik pronounced Chem Chrome-ick a lot like it looks. Protective and Marine coatings. This is an Alkyd metal primer.
First and foremost the stuff is the most bonding product I have ever used and I own a painting company and use alkyd based (oil) paints regularly and have for a number of years. Example: I applied this product to naked prepared metal and in removing some of it, to weld, I learned it was next to impossible with a stainless wire brush in my angle grinders. Apparently this product gets into the microscopic pores in the steel, very pleased with results so far.

Just as important, depending on your view, is that the product is almost completely impossible to tolerate the smell/odor. Again, I have experience with thousands of different types of coatings and none has offended me as bad as this. You'll want to get a breathing apparatus and spare no expense. On top of that the fumes remain in the air for some time. (if the epa knew about this they surely would bury it all with nuclear waste and no one could ever use it again) When I use it again, it will be outside no matter the circumstances. I hope that this is coming across clearly! I'll add that it actually made me angry with a cheapo filtered mask. (the mask didn't filter enough out and the chemical that got into my lungs/bloodstream made me angry) This product will not be used by me inside my shop or any other closed space again, period.

At this point I believe this is and will prove to be the best metal primer available. Cannot reduce.(who wants to have to paint over and over)

The paint (top coat) is a two part product, high solids... The name is Hi-Solids Polyurethane, also protective and marine coatings. Comes with the hardener, one gallon and one quart respectively, and that's how it's mixed 80/20. I'll say more after I use it but SW assures me the odor will be much better and may not bother me at all. I'm very interested in not having to paint again.

Okay, I've added a center single 6 inch channel member for additional support between mainframes essentially making three mainframe beams. My reasoning is that my forklift is 36 inches wide and weighs 5200 pounds dry. I'm surprised that didn't occur to me before. Obviously forklifts concentrate massive amounts of weight in a very tiny footprint... I mentioned the additional beam before but not why. There you have it. (it isn't lost on me that the tandem dually is ideal for this by its inherent design)

I just laid out my conduit and 7-way conductor cable in preparation for wiring. (conduit needs to relax from tight spool position) Here are current images...

Information

I need to add some things not previously mentioned. If you go look at the commercially manufactured trailers you can, or I was, very surprised to see things I would never allow, and that are unacceptable to me. The intent is to pull these trailers down public roads/highways, Safety MUST be a concern. I'm not including the names of companies but the one's I've seen are barely at or just below minimum safety standards to me. It amazes me that people are actually paying thousands of dollars for trailers that cannot possibly last more than 10 years and may well not make it that long or without serious structural issues. Getting up on these trailers and walking to one corner and jumping blows my mind, the opposite corner bounces up and down... Talk about flex!!! Wow! The next thing I noticed was the welds connecting gooseneck uprights to main frames, in some cases there are two single welds running down each side of uprights to main beams with no knees. The dovetails have two center supports only and some use 2x2 angle with 3/16 inch wall. (this is the self cleaning dovetail ramp material) Let me clarify... Tandem dually with 40" spacing between mainframe beams, 40 inches without support, how do we get to 8 feet or 8 1/2 feet (legal limit 102 inches) well to 8 feet which is 96 inches you have no support outside the main beams which are on 40 inch centers, so from 40 inches to 96 or 102 leaves 56 or 62 unsupported inches (varies due to actual spacing but tandem dually axles are generally on centers at 37 to 40 inches and the width of the beams must be considered) in essence you're looking at 34 or more unsupported inches between frame members and 24 or more inches outside frame members. (then the little 2x2 angle on top eight feet long!!!)
The ramps are connected and welded to prevent removing them. Reason? Because when the ramps are flipped over and lowered to ground they support the rear of the trailer by being on the ground, then the dovetail is supported from the ramps on the ground. Fine, but suppose a ramp gets damaged and the customer removes the ramps, then he does whatever he needs to do to get his product/ machinery on trailer. How will he feel when he over stresses the dovetail and/or breaks it off? (worse is hairline cracks and you know nothing, suppose it falls off going down the road???) Do you see where I'm going here? I don't like it. The tandem dually can carry more weight, they have higher ratings per axle and they have four wheels and tires per axle, but at what cost? With the required narrow frame therein lies your cost, higher center of gravity and narrower frame makes the trailer a lot less stable, depending on what you're carrying. Let's face it, we see these trailers traveling down the roads we drive on regularly, sometimes with bulldozers, backhoes, excavators etc.
How often do you see one of these trailers for sale that is over 10 years old? I see a few, but I do not see any of todays big name trailers with 10 or more years on them for sale. Why do you suppose? Why do you think a full steel deck on an equipment trailer is so rare? I'm guessing in order to prevent the deck from washboarding, they would have to use quarter inch plate (or thicker) because the frames are so weak.
Enough of the rant...
I'm using 3/16 inch diamond plate on my deck, 4 inch bedframe and crossmember channel on 16 inch centers, my main frame is 58 inches and each beam is 4 1/2 inches wide. Due to the aforementioned, I added a third main frame beam, a single 6 inch channel in the center, I contour cut the ends and welded into mainframe crossmembers, at the dove I doubled the channel again, welded it to rear crossmember, gusseted the rear crossmember then took 5 inch 3/8 inch wall angle and welded to both sides of dove center mainframe and rear main frame crossmember, I took another piece of that same angle and welded it to the inside of the mainframe dove sections and rear mainframe crossmember.
I'm getting ready to call Dexter and see if I can get 10 or 12K axles with 58 inch spring centers to run super singles like the big trucks and trailers.
I still have the option to add a third axle, though not my preference...
Another thing. The big companies use these huge gooseneck upright to gooseneck forward gusset plates, I believe these are to minimize flex at the neck. Not one to go along, I don't like all that flat plate getting in the way, I cut smaller almost unobtrusive gussets, welded them in that area then miter cut solid 5/8 inch rod and welded to upright and forwards and to gussets and I believe that will stop the neck flex better and look much better, I'll post results...
All of my bedframe and crossmember channel is cut, I'm waiting on a nice warm couple of days, to pull it all outside and finish. I will use the two 7k axles until a better plan comes along or out of my brain. I have the weight at about 6200 lbs currently. 25% on truck effectively removes that weight from trailer axles but in a conservative move, I'm saying 20% and 20% of 14,000 equals 16,800, subtract weight of trailer @ 6200 lbs and I can haul 10,600 lbs.
I am anxious to get it all on the big truck scales at nearby Pilot. I'll weigh truck connected to Goose and goose axle weight, then drop goose on scale and weigh it...