Long story short - I bought an m100 in NC, no title, no bill of sale, no data plates, nothing. (It had been in Saudi Arabia for a long time)
I went to the tag office, told them the situation, and they said they could register it as a homemade trailer.
They gave me a "vin" number that had to be stamped on the tongue and axle, and then I had to get a State Trooper to inspect it.
Was not too big of a hassle, but getting someone helpful at the tag office is key.
My trailer is titled as a 1952 home-made trailer, I can run a 1952 tag like a classic car, and I couldn't be happier with how it worked out.