finding RV value

Along the same lines as K Charles' suggestion, and besides NADA, you could consult a local dealership, and get a sales person to write you up a "letter of opinion" based on what they think it's worth in the current market conditions in your locale. It's sort of a more official estimate of the value of things, from an expert in the field. They see greater usage in other venues like real estate and real property valuations, but differ from an appraisal because they're less formal and complex than an appraisal and use fewer "canned" points of reference or benchmarks. Some folks will do them for free, if they think it might gain them some business down the road.
Sorry to hear the reason you're doing this. It isn't easy.