4 door pickups with diesels are now excellent daily drivers. I went from a 3/4 ton Suburban that got 10 mph to a new Dodge 2500 diesel pick up, with 4 doors and a short bed. The Dodge is still big, but shorter than the Burb, seats 5 comfortably, is parkable in mall parking lots, etc. and gets 20 mph unladen, 14 mpg towing.
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Sorry, this is off-topic, that doesn't make sense. There is no 4-door full-size pickup that's smaller than a Suburban.

An '04 Suburban 2500 (like mine) has 130" WB, 219" overall length.
An '08 Dodge Ram 2500 QC SB has 141" WB, 228" overall length.

So just which part of the Dodge is shorter than the Suburban?

It's true that my Suburban 2500 with the 8.1L and 4.10 gears gets bad mileage -- I get about 13 unladen on the highway, 11.5 around town, and about 8 with the big trailer. But it's way better to drive around town and tows almost as well as the Duramax diesel truck it replaced.

But none of this helps the original poster. I agree that if he's willing to go with a lightweight open trailer, a good mid-size SUV will work great. In my opinion, the thing to avoid is short wheelbases. Long wheelbase makes for towing stability. Heavier tow vehicles are good too (but not so good for gas mileage).