You can check out whether a specific make/model of car can be towed all 4 down by using Remco's online towing guide
. Motorhome Magazine also has lists of towable cars on their web site
A separate, but equally important issue is the towing capacity of your motorhome. The simplest calculation is:
Towing capacity = (GCWR - GVWR)
FWIW we tow a Suburban (weighs 7,000 lbs) behind our motorhome which, using the above calculation, has a 10,000 lbs towing capacity. Of course, it also has a hitch that's rated for 10,000 lbs.
Don't forget the auxiliary braking system for the toad; Check out this illustrated article
showing various options in our library.