I asked around at work and found a guy to weld this thing up for not too much money. We looked at the free trailer and he thought it would be better to just start from scratch, considering the forces that will go through the long frame.
I drew up some plans for the new frame, which will be based heavily on the old one, but will feature an integral (non removable) hitch arm, triangulated truss type design extended forward (but not backward, for ease of storage) and uprights above the wheels to both keep boards out of the spokes and to balance plywood/OSB on top. The uprights will support short pieces of horizontal angle iron so I will be able to bolt in 2x2" boards of whatever length or width works. It should be pretty versatile, with the axle far enough behind the bike that I should be able to carry up to 10' long pieces of wood, metal or even a Human Powered Boat (kayak
).
The great part is that I actually had a bunch of 1x1" hollow square section steel bar lying around and only had to spend something like $35 on new materials. The only part of the original trailer that I will retain is the hitch, which is the hardest part to find/build anyway. The trailer will be more expensive than I'd anticipated, but it should work well.
Also, I'm not getting rid of the smaller trailer- that will get a new pair of (taller) wheels and a new cargo bed, but remain in my stable for more everyday (okay, every few weeks) hauling. The new long trailer will be used for stuff that's anywhere from 3-10 feet long.
Sorry for the novella. I'll post images when we can turn these steel bars into a HPPUT (Human Powered Pick-Up Truck).