We got a signed Certificate of Origin and a bill of sale when we bought our Lance 845 new at an auction (Lance warrenty included). We made a copy and still hold the original too. We are not required plates for a TC in Florida. So, a bill of sale is sufficient to sell. I have no clue how to check for lien, altho, if a lien is on any RV or TC, I'd expect it to show at the registry.
I recently transferred to a Florida plate for my cargo trailer (bought in Mass a few years ago,) and the Registry only required a Certificate of Registration in Mass to issue new plate. She went on the Mass RMV site to look for liens and valid Registration in my name. Came up clean, so she handed me a new plate for some $$$ ... took five minutes.
That means to me that RMVs have ability to verify or check for liens. My guess if she found a lien, we'd have had to clear it before she'd issue new plate ...