More doodles... this is a scale study. Note: a very ROUGH scale study.
Also, in the shot above the lid is just over the center section, however, I think I will make the lid the entire top of the trailer. The price of good latches has helped make this decision.
All these concepts were created in AutoCad .00001![]()
Our Horizon has a drop down rear door...I would prefer, however, to have a vertically hinged door. Either way FYI we use the door rather than the hinged top to access the cargo box contents 90% of the time (but use and need them both). Also REZARF, above, you mentioned screwing aluminum plate to your 1x1 frame. I would use steel and weld it in place (or use aluminum tubing and aluminum plate). Screws = maintenance at some point on a trailer that will see it's fair share of vibrations.
And, although you have probably thought this through, use high quality automotive type weather stripping on all doors/lids.
Just my $.02