For long hauls and fuel economy you can't go wrong with the VW Jetta TDi Wagon. If you prefer the automatic (maunal is best) it will take some getting used to as the shifts are firm and sometimes searches for the right gear. But, long trips will reward you with 40-50 mpg, loaded or empty. That's just the way diesels are.
Make sure there is some kind of engine warranty - not for the engine but for the high pressure fuel pump system. VW, in order to save money, uses plastic internal parts and there have been some cases of catastophic failure at speed. The parts disentegrate and you will be looking at a $6 - $8k repair if not under warranty. Not just the fuel pump has to be replaced - injectors, fuel line and in some cases the fuel tank. Not wishing to scare you away from a wonderful car, but this has happened in about 3% of the vehicles. The VW dealerships have been selective in considering it a warranty issue, citing "bad fuel" as a reason. BS.
I have an 07 Touareg (V-10) TDi with 170,000 miles. It has the same high pressure fuel system and I have had not one problem with routine maintenance. While the V-10 is not very fuel efficient as far a diesels go (average about 20 mpg overall) it will dry-dock a battleship and outrun a Mustang GT. My fingers will have to be pried from the steering wheel.