Fuel stabilizer is a must, and put non-ethanol in the tank if you can find it. The new ethanol gas undergoes what they call "phase separation" after about 3 months. I don't know enough about it to explain it, but I know that it will wreak havoc on your engine. Other than than, wash and wax before you go, and make sure the truck is dry so you don't have to worry about rust. Change your oil, and consider leaving the truck on jack stands to avoid flat spots on the tires.
I remember a thread a while back where someone asked a similar question, so a search may turn up some more tips for you, too.