I don't know nothing about SC law, but would assume if you finance the fifth wheel the financing institution will require it to be titled (in my home state you can title a vehicle/trailer, etc and not put license plates on it), We are currently in Florida but maintain our residence at our son's house in Missouri. We don't take the rig back, so all we use it for is voting, paying property taxes, etc.
Sounds like you need to speak to the supervisor of what ever county offices you are contacting. Someone there is not doing their jobs if they couldn't answer your questions.
2015 Chevy 2500HD 4x4,2008 Crossroads Cruiser M29CK, 2008 HD Ultra Classic Trike