With all this fabricating needed. How is the under carriage/ rear bumper area to try get a receiver hitch fabbed on their to hold a bike rack. That way you wouldn't be compromising the water proofing of the top.
Reading forums apparently this is not a great idea, because the structure isn't that strong.
Found a picture earlier while I was at work of a padded wooden frame that has a couple of steel bars running across it that I could attach my Thule racks onto. Then the whole thing is strapped around the trailer with cargo straps. It's certainly a less invasive solution than bolting through the roof, but strength could be an issue.
This was another idea that could be pretty cheaply knocked together:
https://onedrive.live.com/?id=340B86F54757E2F0%21120[HTML_REMOVED]cid=340B86F54757E2F0
Being cheap is OK. Being a clueless sanctimonious condescending douchebag is just Vlad's MO.