It's not too bad, as a prototype I'm pretty happy with it.
A couple of things I would change if building again:
1. I would have the tow bar extend from the top of the trailer frame not the bottom, it would improve ground clearance on the back
2. I would probably use 6061 instead of 6063 aluminium for a bit more stiffness
3. I might use fully square tubing instead of rounded corners, it's cheaper, stiffer and I really don't think it would scratch anything up
4. I'd consider buying two kits and having 4 wheels placing them right next to each other, currently the wheel loading is pretty heavy
5. I'd make the ama supports detachable, it would make it easier to use the trailer for other things
6. I'd add a brace for the towbar, mostly up/down but also stiffen it for sideways movement a bit
This is the kit I used, I only bought one but if you don't want to do any welding you might just be able to buy multiple kits and parts and bolt it all together, I wish they had aluminium brackets instead of the black plastic but I guess at this pricepoint it's hard to justify.
https://wikeinc.com/en-ca/products/cargo-diyIf you feel like picking up a welder I did the whole project with a $500 AC/DC Tig welder I ordered off Amazon, granted I have a fair bit of experience but I had no tools here on the island so I just got the cheapest half-decent inverter machine that would get the job done.
Let me know how it goes and if you want me to send you the exact dimensions I can dig up my drawings and send you a diagram plus BOM.
Antonia