. . .I have a quad cab truck and often have to fill the center of the back seat with gear. Though I am thinking of adding a Taneau (totaly misspelled that word) to give the truck a bigger storeage area.. . .
The word you're lookin for is "tonneau" cover, although "truck bed cover" is a better description. I have one on my Ford Ranger; it allows me to carry a lot of gear year round. Highly recommended for those of us with trucks that only haul small stuff.