Bookmark this page in the forum.
For Sale: Molded Fiberglass Travel Trailers - Fiberglass RV
And this site
Molded Fiberglass Trailers | Fiberglass RV's For Sale
Both are good starting points for your search. Check them often and expect to act fast if you see something you are interested in.
Craig's list is also a possibility but beware of scams, have been several reported specifically involving FGRV's.
You might also want to print off this check list for inspecting a trailer.
On older trailers frame for cracks, axle
for suspension sag on old torsion axles, and floor for soft spots. Especially around the outer edges inside where shell meets floor. Water from leaks
generally follow the wall down.
Good luck on finding your perfect camper, but I have to warn you having kids stuffed into car with camping gear does tend to reduce the "he's touching me" events due to not being able to move. ;-)