IMO, the key to selling a vintage trailer for top dollar is disclosure. The more information and pictures you can provide the potential buyers, the better...especially with the internet market. You have to figure, an internet buyer has to take your word for the condition and without pictures to back it up - that's kinda difficult.
Also, making it available for inspection helps. AirForums has a network of folks willing to help buyers by being their remote eyes & noses. Here's a checklist
of what they may be looking for - it would be helpful for you. so you can address these items in your listing or are prepared to discuss them at a viewing - regardless of where you list it or how you price it.
Another great resource is this Price vs. Condition
Good luck with your sale ~