You can build your own uniquely curvy top half for this thing with polyisocyanurate rigid foam and fiberglass mat or cloth. Build a temporary armature/boat skeleton structure on top of this base to support the foam from the inside. Keep perfect matching mold forms from bonding by using two layers of aluminum foil to separate the two sides. Window, door, and vent openings, curved or flat, can be framed by multiple layers of plywood laminated together so you have a very solid screw base to attach things to. Attach the window frames to the armature. Lay on sheets of foam, using 2" or thicker to radius tight corners and curves, like building a barrel with thick foam staves. Glue the foam pieces together with contact cement and stainless steel screws, and shape the outside surfaces with surfoam tools and sandpaper.
When you have the shape you want, laminate the outside with fiberglass. I used minimum two layers of 1.5 oz mat and did not try to sand it smooth. White gelcoat sprayed at a slight stipple finished the outside surfaces.
After the outside is laminated, disassemble the armature and pull it out. Shape the inside surfaces as you like, always leaving at least an inch of foam, (2" or more is better insulation and stronger). Embed plywood strips for screwing interior features into as needed. Fiberglass the inside. I turned my camper upside down to do the inside roof.
Now you have a curved camper shell that is insulated and self-supporting ready for interior furnishings. I used redwood bender board radiused in inside, standard trailer awning windows
and 14x14 vents, and a wood/foam sandwich door. I built my foam sandwich stand up pickup camper in 1972, lived in it for more than 7 years, and still use it today for camping and job shack.