Our 'best' road trip vehicle has been a Chevy Express 1500 cargo van. This is our second one, a 2007. We go out for 6-8 wks, currently out for 12 wks. In our first van, a 1997, we built a platform, like you mentioned, and it holds 2 twin mattresses. My 6'3" husband fits fine. We also have a kitchen cupboard to store Coleman stove, pots, etc with a microwave on top. We electrified it for the few times we get hookups. We mainly camp at federal sites.
Gas mileage is 20 mpg. We appreciated the high clearance, not 4WD, but gets us back into some out of the way places we frequent.
The best part is when we got the second one in 2007 the interior dimensions were exactly the same, so everything fit in the new one with no modifications.
Another modification we did at the beginning was to put 3 RV-style windows(sliding with screens); 2 in the back by our heads where we sleep and 1 behind the driver seat for the 'kitchen' area. When we run this one into the ground we plan on doing the same thing again - it works for us!
