My thoughts for pondering. If definitely towing with dolly, consider a Grand Caravan. FWD, and has the stow n go seating. We have one and love it. However, what is your RV rated for towing? typically for a gas A 5000 lbs. The tow dolly adds about 4-600 lbs.
I do not tow mine, I tow a car that can be flat towed, although we kind of miss having our van with us.
Buying used, check with the local RV dealers, they often take in cars in trade that are set up for flat towing, make a friend in sales to keep an eye out for you, offer a finders fee. Watch local ads. My toad I found on Craigslist and was all set up. Also watch eBay or local for a brake buddy type system,, easy to use, no mechanic needed.
If you find a car you like that fits your needs, but no baseplate, decide whether or not you want to make the investment in one. Install should be done by pro, it is quite involved. I work as a tech in a dealership and have watched the job. Some cars can take a full day. This is why I suggest getting a car with it installed. (dealerships usually wholesale the cars out, they aren't in car sales business, but will sell if you can get that in with someone.
4 down is so much easier than dolly. I work mainly in new owner instruction and one of my customers just bought a dolly. Nice one, but he could not move it. On pavement, not bad but in gravel just about impossible. You would ned to carry along a dolly-dolly. A wheeled device so you don't have to lift the tongue by hand.
The issue of where do you store the dolly when you get to destination, where do you put it. Some places you have to store off your RV site, some you can keep it with you. If you do go the route of a dolly, be sure to set the car up for towing so you can move it around.
Brakes on the dolly, there are surge, where the weight of the dolly pushing against the hitch as the rv brakes, will apply braking to the dolly, and there is electric brakes, requiring wiring in a controller on the dash of RV. These run about $100 - $200 plus install.
Used units are out there, make sure to check tires and overall condition, especially the straps. Plus check straps after a few miles of deriving, they almost always will loosen up a little, and check every 100-200 miles as well.
Good luck in your search.