I've built and / or modified some trailers over the years. First off, I'll say that I'm not a fan of seatpost mounting, and use only axle or chainstay mounts. Also, I've long given up trying to make safe and practical hitches, and have used mainly Chariot hitches over the years.

The first two trailers were no-welds using conduit for the frame and slotted elec. box covers for the dropouts. I got the plans from an old book titled "Build Your Own Carts and Trailers". Details on two of them are at my website: one small and one much larger.

I've since modified two other trailers, a heavier one with steel frame and wood sides, and a lightweight one with a box made mainly of coroplast (election sign stuff). My blog also has posts of no-weld trailers built by others who sent me their photos, under the trailer tag.

The above are all great, but when I really need to move stuff my homebuilt e-assist cargo trike gets the call. (Trike blog tag)

Mark