Hopefully a couple of other angles will be easier to make out what I'm working with. I've considered things from just leaving it flat with minimal siderails with a tarp to something like a utility truck bed by enclosing the tires and making the whole thing follow the suggested template with a removable lid. The only other regular use this trailer has is taking off the garbage, because I don't have a truck.
The trailer measures 7ftx4ft at the base, and from level ground the top of trunk measures 42 inches while the top of the trailer sides are at 52 inches. The mocked lean at the rear measures 48 inches at the base with a slope to 36 inches at the clamps. I only have about 28 inches from the inside of the base to the top of the sides if I left it all square, but I'm willing to lose a few due to sloping.
The base is stainless steel from a job, and it's installed on the bottom lip of the frame for streamlining underneath, which was a fun afternoon... The large sidewalls are the aluminum sheet base when I bought the trailer used, and the permanent sidewalls are 10 inch galvanized heavy gauge metal studs. I'm planning to use the same studs for fabricating a rear frame for access, as well as the wall/roof support and other stainless as the top and front.
I'm planning on a tailgate type access panel or maybe french doors for the rear with a minimum size of 36 inches wide by 24 inches tall. I've considered a clam shell lid or installing the access panel on the sloping roof but those would probably increase the complexity of actually loading and unloading for regular use.
I'm assuming a proper curve rather than an angle would be best for the front of the trailer where the air leaves the car and meets the trailer. I'm willing to lose a bit of space between the car and trailer, but I can currently back the trailer up considerably farther than 90 degrees, and it's quite useful in tight locations.