ghcoe,
Andrew is spot on about those tight radii. Aesthetically, I find them very pleasing to the eye, but technically, they are very hard to construct uniformly. The Euro-style caravans you referenced are factory produced with molds and jigs. Assuming wood construction for yours, you would have to dado two edges in over-sized lumber to carry the plywood flush and then shape the lumber with an electric planer and/or a hand-held grinder with a sanding disk. This alone is a very complicated process. Also, lots of finesse and a template are required to make them all the same radius. It can be done. But is it worth that much extra work?
Another issue, previously mentioned, is resale value. Yeah...when we're building something special for ourselves, it takes on a very personal, even spiritual dimension (if you will). Then it seems rather meaningless/shocking/insulting to think in resale terms, but consider this segue: What if YOU change tow vehicles out of necessity? Will that short tongue design with a cut-under front work for turning when towed behind a station wagon or a pickup truck or a small SUV
I dealt with largely similar design issues as you in planning my build ROUND TAIL. The only significant difference between ROUND TAIL and your design parameters is that mine is 6 foot-6 inches wide. I did the same thing with the door and standing headroom as your design. Check it out. (See clickable link below.)
For what it's worth.
Best wishes to you,
Prem

My goal...
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...is to live in a trailer.