I found one of those tag-along kid trailers at a garage sale and figured I could make into something I could haul gear around in. Here is the first successful iteration.
Stripped down - 8 pounds less..
Early testing version
It has proven surprisingly strong and rigid. I've only done preliminary test riding with it and it has worked well. It will bear my (Clydesdale) weight. I'm refining it to improve the aesthetic though this is functional. I've not seen the need to reinforce it though I plan to add some aluminum angle.