Neale, as you noted it really depends upon the state you are in. They key is getting a title and a bill of sale. If the plates don't stay with the trailer, you would be able in most DMV offices get a travel permit which you would either mount on the back window or secure to the license plate holder. Personally, buying from out of town site unseen carries some risk and I would advise you to either look carefully at what you are buying personally or obtain an inspector to help you. Obviously your vehicle must be prepared to tow your purchase back to you home so pay attention to that aspect of purchasing out of town.
As a new Forum member you might also place your topic of interest into the subject line of your post rather than your screen name. That way you will get more responses to your questions.
On the portal page on the lower right side you will see a search feature to help you find inspectors. These are members from the Forum who are willing to help you look at trailers or motor homes that you might have interest in. Bottom line though I'd still consider you travel if necessary to do the final look.
'04 Classic 30' S.O.,'03 GMC Savana 2500,'14 Honda CTX 700