Figure, the axle is wide enough, with enough of a weight capacity... right? We're talking small and light cars, of course.
The midwest has millions of little lakes and every fall you see the Boats and trailers "For Sale" very cheap... ($100- $900) And I have modified several trailers for hauling cars and Lumber...!
My 2 axle car/utility trailer is made from a boat trailer. I used the shit out of it. I even hualed a '51 Caddy hearse on it, but that was a little sketchy.
I have one to bolt a body to while working it also can tow to sandblaster etc just finished a 40 ford sedan on it now putting a 40 stude coupe on it sits just right height to work on and with the drop down third wheel up front that swiviles ala harbor freight, i can park it anyuwhere i want to , roll it out blow it out or hose it off etc . ...........
Car dolleys have restricted use in our hobby since any car that has even one wheel on the ground has to be legally insured and licensed for the road. In other words, you'll get tickets right and left if you haul "projects" around with it. If you do it, use one that already has a :Never needs renuing" plate on it and keep the trailer VIN on what's left.
Your milage may vary. I can't tell you how many zillion times I've been passed by cops even rolling down the Thruway with a car flat towed behind me, no plates, no insurance, nothing. A dolly itself probably needs to be registered as a trailer, though. Last place I was that used one regular was the college, theirs didn't have plates, but then again they used to drive the new cars back and forth from lab to lab that were donated by GM never to be titled or driven according to the big stickers on them. Of course in this state some trailers can be moved without plates, too. It more than likely depends on your state or country laws -
No, I'd register the dolley... It would be for dragging donor/project cars home... My insurance, AAA, gives me a 9 day "grace" period, where anything I purchase is automagically insured for that length after date of purchase. Now, I'm sure dropping something off of a trailer, especially a homebrewed POS, may prove interesting...