Zeb-
I built a drawer for my Suburban with almost those exact dimensions. I will try and take a pic tomorrow to show you.
I used 2 x 6s on the sides and then bought the most heavy duty drawer glides that Home Depot had. They were about $26 for the pair. The drawer is made of 1 x 6s ripped down to 5 inches and 1/2 inch plywood. I have a latch that keeps the drawer closed. It holds a ton of stuff. It can take the weight of a lot of ammo, but I try not to put too much in there. I also made a couple of wood dividers in the front for small stuff.
You will have problems with the top sagging if you do one drawer unless you get some high quality plywood. I used a special plywood made for outdoor signs that my dad had left over. Regular plywood did not work put the sign type did. That plywood might cost you a bit more but you save $26 on a pair of glides.
The main complaint I have about mine is weight. I can't really load it myself without risking a back injury. I would see if the sides could be made of 1 x 6s instead.