Most trailers that are solid and leak-free also have a full interior. Rotten floors caused by leaks
are the usual reason someone would gut a trailer. Never know, though- you might happen across a half finished project.
Know that in most molded fiberglass trailers, at least some of the interior components are structural. Since there is no frame in walls or ceiling, cabinets serve to stiffen and support the shell. So you'll want to keep at least some of them in your studio.
Depending on your budget, you could take a look at the Happier Camper HC1
. It is a new design with a completely modular interior.