as in many answers.....it all depends....
If you tow "all four wheels down" You need a tow bar (Blue Ox or Towmaster sort of equipment), you need a base plate attached to the toad (these are car/model specific), and you need an ancillary braking system (either a Brake Buddy sort of equipment or an SMI "Stay and Play" sort of equipment) The Stay and Play works automatically when connected to the MH without having to move equipment into or out of position relative to the Toad brake. Pluses are that you don't have to try to figure out what to do with a trailer when you arrive at a campground and it is simple to connect and disconnect. Negatives are that you CAN NOT BACK UP if you end up driving into a lot that doesn't have adequate turning around area.... Only certain model of vehicles can be towed 4-down without additional adaptation. Some not at all. Towing 4-down does not effect your car mileage but does add mileage to your car tires.....
Start watching the interstates as you drive around......Some folks tow with the entire car up on a small trailer. You have to load and unload the car from the trailer if you want to use it. Depending upon the site you are parking in you may have to disconnect the trailer and park it someplace in order to park your RV at small back in sites. Towing the car on the trailer will not add wear and tear on car tires. Towing a trailers does allow one to back up as well as any trailer back up.
Some folks tow with just the front tires up on a small trailer. The ones I see loo like it requires a lot of straps and hooks to make sure that the car is secure on the trailer.
It is all fun.
Several of the folks here have been fortunate (and/or researched carefully enough) to find used vehicles that already have a base plate on them.
Several of us tow 4-down. Anybody out there tow with a trailer that can jump in with personal experience?