I still have two angled braces to add, but I tested it with 285lbs of bricks and old SLA tossed randomly into the kennel, and rode more roughly with it than I would with dogs in there, and didn't break anything, though the load shifted a few times. (had to measure two fo the SLA separately, cuz the scale doesnt' go that high!)
The trailer itself at this point weighs around 55lbs, not including the lights and wiring, hitch lock and security cable (just in case something happens to the hitch, it ties the frame to the bike's frame), which all together are probably a couple more pounds.
The hitch tongue is bolted thru the top of the trailer tongue, and also spot welded at it's rear corners. I messed up on making the trailer tongue, though: I marked and cut the side angled pieces so they'd go past the 45-degree brace under the tongue, but somehow I managed to cut them about two inches shorter than I marked them, and I don't understand how I did that.
Well, anyway it dosn't matter cuz I am still gonna add a 1/2" square tubing brace down form the rear end of each of those tongue-sides, to the front corners of the frame itself, ot minimize any side-to-side wiggle of the tongue vs frame.
The major issue with haivng the tongue go up from teh trailer is that the door to the kennel only opens partway: it's more than enough for either dog to easily go in or out, but it's a little annoying. I tried to figure out a way to keep it strong and to leave the door clearance, but no matter which way I did it (even at a 45 degree angle instead of direclty upright) it'd still stop the door right at that point, unless I had it straight out from the front of the trailer. That won't work easily cuz of clearnace issues with the bike itself, so, I left it like this:
However, despite it not having any detectable issues with the wheels/etc during or after the test run, I found that if I accidentally drop the trailer on a wheel (which happened as I let it down from the hitch point I stood it on the scale with), it'll bend the U-fork right good, sending the wheel canting inward at the bottom by a LOT. It did not affect the wheel itself, so I guess I tensioned it right.
So to prevent that, or minimize it, I'm gonna have to add the vertical U over the top of the wheel at the dropouts, as I had pondered in the OP. At least I found out now, instead of on the road with a load (like the dogs) in it.
Speaking of wheels, I siad before these were steel rims, but they are not: they are aluminum, doublewall, actually, and are 48 spoke not 44. Thy're the old BMX wheels I originally used on the "chariot" trailer I built for DayGlo Avenger, and sat unused for a few years now, since I made the other flatbed kennel trailer MkI. I don't remember the spoke tension being almost zero, but when I started working on the wheels to replace the bearings (some of which were damaged, along wiht one of hte axles, in a bearing-cap failure on the chariot trailer), I found many spokes so loose they rattled around. Rims weren't bent, so ti was just lack of tension.
After replacing all the bearings (and regreasing) and the axles and nuts with ones off other old wheels I won't be reusing as wheels, I tightened them up, and trued the rims, so they should be good for a while now.
I also notched the kennel itself, so it fits down into and latches onto the frame. Now it does not have to be bolted on at all, and will be removable when empty if I need to make it into a flatbed, much easier than unbolting it. It also sits much lower on the frame, so combined with the lower frame itself, it lowers the entire COG of my loaded trailer, *and* it brings the top of the kennel down way below the lighting bar on teh bakc of the bike's seat, so youc an clearly see the brake, tail, and turn signals on the bike, too, from any vehicle that's behind my conglomeration.
I added a brace under the front of the kennel so it can't sink down between the frame, too. It goes down in a squared-off-U between the forks, and also serves as an extra brace for the frame at the wheels. I was gonna stick it under the front edge so it also cannot possibly slide forward, but that didnt' work out, as it would keep me from sliding it forward to take it out of the frame, too.
I still have to make a flatbed cover for the frame that "latches" on, but that's not that big a priority yet, as I usually use it for the dogs or use it with teh kennel as a locking cargo container.
I also still have to make a rear mounting bracket for all the lights, and an SMV sign (which I also sitll have to get, or maybe just move the one I have on the bike to the trailer when I am using it); for now they are ziptied to the back of the kennel itself.
To connect the trailer lights to the bike, I used a 5-pin DIN, like MIDI cables or the old AT-style keyboards used. (mostly because it has enough wires for tail, brake, and L/R turn signals, and because I already had the mating ends on DGA from the old trailer). I'ts not waterproof or anything, but it is fairly durable and takes a fair bit of plug cycles ok.
The lights themselves are the ones off the back of Delta Tripper, but with the incandescents in teh turn signals replaced with LED units intended for a Fluval aquarium (to replace little 12V MR-style halogens). If they hadn't been clearance cheap they'd've cost way too much to use for this, but I got four, and eventually they will go on the actual bike itself, when I get to it's rewiring. The paper towels jus tkeep the bulbs from shifting around under vibration.
Oh, and performance of the bike pulling that 340lb load: 69.4Wh/mile!
Yeah, it sucks but it can do it!
Takes like 10+ seconds to reach 20MPH from a stop, vs 3-3.5 seconds with just the bike.
Actually got higher regen currents than usual (double what I typically see on my commute); I wonder if that was because it was being pushed harder from behind while braking?
Short of any replies about the hitch, and needing to make *something* to use so I can work on carting the dogs around now that the weather is cool enough, I went ahead with the "L" going up from the trailer frame to the hitch ball on the bike.