Either size vehicle has it's merits. I've been happy with my full-size van (aside from the mechanical/electrical issue I have going on). A full-size with regular body is surprisingly maneuverable and fits into most places. You can put a Thule box on the top and it will look like the family truckster! My Chevy with a 5.3L V8 gets 20-22 MPG if I keep the cruise at 57-60 MPH on the highway.
One suggestion if you plan to stealth camp is get the windows starting behind the front doors treated with limo tint. You can do curtains/blinds as well but mine has the limo tint and you can't see anything even with your face pressed against the glass during the day. At night, you can see in if there is a light on inside so that is where the curtains will help. Then install a curtain behind the front seats creating a sleeping compartment. Looking through the front windows, the vehicle apears vacant while you sleep, read, etc. in the back.
I would also cruise through the Storage Solutions forum to give you ideas of how to build out the back end.
Have fun!