You need to make sure the Grand Cherokee has the Quadra-trac II transmission which has the transfer case that will allow you to tow behind your RV. Quadra-trace I is NOT towable.
I just pulled my 2008 Grand Cherokee 6000 miles with zero trouble.
If you are looking at a used 2006/07, I HIGHLY recommend trying to find a Grand Cherokee with the 3.0l CRD Diesel. It is a Mercedes engine, 23 mpg, and runs great. My 2008 was the last year they offered that engine.
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
RVing for 19 years & 150,000+ miles