-American BOF cars from the 90's (install tranny cooler if they don't have it)
-Volvo's; 3500lbs towing, wagons have self leveling suspension in many models, transmission and oil have coolers factory installed
-Subaru's, 2000-3500lbs towing, cheaper to run, completely gutless tho... not as nice to drive. May kill the transmission (install cooling if not in place)
Or you get a fairly cheap truck (with gas prices climbing, won't be hard)
... Your mileage will be not much better then 20-25mpg combined with anything with a tow rating. You might push high 20's to 30 on the highway with some of them.