This is by way of testimony, not of advice. On exactly ONE occasion in the nine years we have been traveling with a fifth-wheel we could have used a 4 wheel drive vehicle. On that one occasion the park rangers got us out within 15 minutes (a quick rain shower in Manatee Springs State Park in Florida--wrong campsite for those conditions).
That means I have had nine years minus 15 minutes of not having the added expense, limitations, and potential problems of a 4X4.
This is my testimony and not intended to influence anyone else's decision. For me, where I live, and how I travel, this is the right decision. For others the choice would be entirely different.
David and Shirley -- East Texas
2955 RL Montana
Chevrolet Duramax 2500 Allison Trans
http://www.dwilliamson.com/mont.jpg