Selling value of RV
You could also do a nationwide search on Craigslist using a site like SeatchTempest as well as RV Trader for your make and model to try to see what asking prices are.
Along with NADA, that should get you in the ballpark. Location, season, and, of course, condition have to be factored in.
To clarify, the focus of this forum is all-molded fiberglass ("egg") trailers, which are different from fiberglass-skinned stick-built or laminated trailers.