Browse
https://www.fiberglass-rv-4sale.com/...-trailers-sold and you'll find that there's no rhyme or reason to current asking prices. In 2019, your trailer might have
sold for $9-$10k. Today you should easily see 50% higher. You can always list high and see if anyone bites. If not, wait a few weeks and take the best offer. I would advise avoiding buyers who low-ball you but promise "cash in hand at your door tomorrow." While they may deliver, most likely they will just flip your trailer at a profit with nothing but a little patience.
I wouldn't feel guilty about turning a profit on a trailer right now. It's a luxury item, not a necessity.
If you haven't contacted a builder, you're in for another surprise. Any profit you feel you're making on the trailer will evaporate with the higher material costs we're seeing.