The more I think about it, the more I like your CRX trailer and find my design converging on it, aerohead. It's an elegant solution.
This is what I'm up to now:
I decided it would be possible to keep the rounded nose so long as I didn't slope it at the top, which would require that I cut two fitting ovals. Turning angle is down to 65° if I don't set the nose back, but I'm thinking of constructing the trailer with a plywood frame, bottom, and lid, and siding that you'd use in an RV shower which would give and return to shape if it hits the bumper; plus it's waterproof. 7' length keeps the slope shallow enough that I should hopefully have reattachment of air before the tail end, and lets me cut it from two 4x8 sheets of plywood. I don't think I'll be able to easily round the top edges like you did.
What I haven't decided on yet is what to do about the fenders and underside. As I understand, extending the fenders down to cover the front of the tires should provide aero benefit, but that might be a bit ambitious for my first iteration.
EDIT: I miscalculated the volume of my design #2 in post #33, it should have been 22.5 cubic feet. Volume of this design is ~32 cubic feet.
EDIT2: Should I lower the front an inch or two, do you think? The leading edge of the cylindrical nose is within the template, but moving back, it's not.