What to look for when buying a used T@b trailer

Hello all, I am just beginning my search for a gently used 320 S. I want to do my due diligence and ask all the right questions. Can you point me to a source, checklist or consulting service to help me make a good choice? I've been burned in the past (when buying a vintage camper) and I don't want to repeat those mistakes. Thank you in advance!