I've learned a few things over the last few years about tow rigs, MPG, and the like. We have a 1995 Subaru 2.2 that we occasionally tow with and a 1998 Sienna that is our primary raft/ camp vehicle. The Subie gets great mileage, and I'm a Subie Lifer, but I need capacity, as it is always the four of us rafting at least in the summer, plus we need space for shuttle duty.
So the Sienna does most of our raft towing. It gets 20 towing the raft, rigged for a day trip. If I have it packed with camping gear, I usually am headed to the mountains, gaining at least 3000 feet in elevation on the drive. Then I get 15 mpg. I almost got stuck on a ramp with it a few weeks ago, I wished it was AWD like my Subie.
My Dad has a Suburban. it's a 1999 with 191K, and 4wd. He gets 15 mpg with it, even hauling a small camp trailer or raft trailer with lots of gear in the back with the 3rd seat removed.
I want to get a Suburban as a 3rd vehicle mainly for rafting and camping, and let it sit when the capacity isn't needed. My 3 liter V6 is working harder when we climb a pass, his Suburban is loafing along like it isn't even trying. His seating capacity matches my van's.
An AWD van like a 2004 and newer Sienna might fit your needs, as those have a large increase in power and AWD, plus seating. I would probably do well with one of those, but I want a body on frame 4x4 this time around.
Our Sienna will do for now, it gets in the 20's when we aren't towing, it's cheap to maintain, and it's a great kiddie hauler. I may add Firestone coilrite airbags to the rear next season, but camping season is over for 2013