Crunching the numbers the Merc might not be possible if you coach hitch is only rated for 5000 pounds. The car plus a trailer is going weight more than your hitch and likely the coach can safely pull. So you'll need something else in the driveway and the lower the cost the better.
Before you start shopping you'll need to decide on four down or a dolly. A dolly will give you a bit more flexibility concerning a third vehicle. Any front wheel drive vehicle can be towed with the dolly (some hybrids can not) without any modifications but the dolly is a bit more work at the camp site. If you go with a dolly have a class I hitch installed on the tow car so you can use it to more the dolly around.
Four down narrows your car shopping choices and requires a bit more stuff (tow bar, base plate and possibly a braking system) but is much more convenient while on the road. Four down can cost a bit more initially than a dolly especially if you have the base plate installed but once everything is set up you're done.
Which direction you choose to take, dolly or four down, keep your costs down and buy a used vehicle a few years old that you can use more than just while camping. My vehicle of choice is the Honda Accord, CRV or even an Odyssey minivan. Some of the Saturn's were built using transmissions from Honda. Jeeps are also a good choice but can be a bit heavier than a small car. Don't assume a manual transmission can be four down towed either. Granted 99% probably are but verify just to be sure.
Good luck with your search.
