Lynette;
While NADA guides or Kelley BlueBook or other guides might give you a range of prices based on dealer input (Dealers are the ones who set or send prices to these guides), they are for dealer benefit and financing, not consumers and private sellers...
That said, potential buyers might also go there and be put off if your prices are way out of line...
I'd look at big 3 for electronic ads (Here, Vintage Airstreams at
www.airstream.net, and rvtraderonline.com ) and see if there are any similar trailers in your area, or even if not similar, how they are priced relative to NADA or kbb guides... Whether selling by placing ads or E-Bay, set price slightly above mid-point to test market first and give yourself room to make concessions, unless you are in big hurry.. I'd also have someone else do thorough inspection, with objective eyes, so you aren't biased in thinking yours is too wonderful...
Finally, if you're selling, the wider market you can reach, then better chance of selling for a higher price. A local newspaper ad will reach a few potantial buyers, while a listing here and one or two other web sites might reach 80% of those looking for a used Bambi...
John McG