You might get in touch with Weiscraft or Pelsue and ask them if they will sell you a bare shell trailer.
Lightweight Trailers - Compact Travel Campers - Weiscraft Trailers
A bare bones Little Joe
(Weiscraft) would probably suit your needs.
The Pelsue Fiberlite is an aluminum framed trailer set up for telecom cable splicing.
Both of these companies are located in Colorado, so pickup for you wouldn't be too great a stretch.
Note: Most if not all fiberglass trailers do require some interior framing to support what would otherwise be a very flexible shell. Usually this is accomplished with interior furnishings; shelving, cabinets and such, much of which is also made of fiberglass for the sake of strength and light weight
. I think that I would be looking at buying a trailer with at least these basic accouterments, without cutouts, so that you could modify them to suit your particular needs.
Good luck in your search. You can get a better idea of the Little Joe
by looking at the pictures in the Gallery. You can also look at the Lite House
, the original incarnation of the Little Joe