In answer to your other question, yes, there is a robust resale market for used 13' molded trailers. See the classified ads and sold
archives on this site and at www.fiberglass-rv-4sale.com
to get an idea of values.
The market is cooling with the weather, though, especially in northern states, so you might do better waiting until spring to sell. Use the winter to prep it for sale- take care of any maintenance issues and get it looking its best.
There are larger molded fiberglass options you might consider. Molded fiberglass trailers do have some distinct advantages over conventional travel trailers: easier towing, fewer places to leak, and strong resale value, for starters. This forum is the best resource on the web for all things related to molded fiberglass trailers if you decide to go that way.
Welcome, and best wishes!