I have a 20' tilt deck trailer with carries my LJ plus a couple of motorcycles but have been considering a car dolly for pulling behind the motorhome. When I am not dry camping in the desert, the trailer becomes an issue in campsites. The car tow dolly would be much shorter to stow while not using it.
Never owned one, just trailers. Downsides to a Car Tow Dolly? Flat towing seems to cup my front tires.
Car dollies are great for moving 2wd cars. So much lighter than a full trailer!
If you wanted to go as light and small as possible you could use a tow dolly and high speed dolly to get the rear tires off the road. Or use the high speed dollies front and rear and a tow bar. Theoretically, anyways. I've never seen anyone do that.