I wonder what would happen if I was to build a cabin with wheels under it? I'm not planning to do this, but that would be a "portable cabin", meaning it could be moved. I wonder how that would qualify, regarding a title?
I have seen this done. Some guy bought some land to hunt on, and did not want to build a permanent structure. He build a rather nice cabin on the frame which I believe came from a semi-truck trailer. He had a hitch on the front, and stored it on his land, but he would also haul it and use when he went camping. It's my opinion that this would qualify as a RV camper, even though it was home built. I spoke with the guy when he was at a campsite and got to see the interior of it. He built a really nice cabin, and I was impressed. But I never bothered to ask about title or licensing at that time.
I have also seen people get a trailer home, and build it into a house. In fact I visited some people once who had what looked like a regular house from the outside, but when you got inside there was a trailer inside of it. They said that they originally lived in just the trailer and kept building around it until it became a house. It still had many of the trailer rooms inside such as the original bathroom, but the trailer was completely enclosed inside the house, including a roof over the entire building, with the original trailer roof now inside the attic.