Even without going to bigger tires, if your going to but on bush gaurds and racks then a rear tire/gar can carrier rack might be beneficial. A quick google search brought up this http://www.coloradok5.com/projects/beasttirecarrier2.jpg
I put a tall cap on the back of my truck so I could have soe covered storage and plan to build a rack something like that to get the spare out from under the bed. Then I can put an additional gas tank under the bed where the spare was and maybe eve still have a gas can or two on the rear carrier. I'm just trying to decide if I want to make the rear carrier plug into the trailer hitch which prevents me from towing a trailer or mounting to the bed (with reinforcement inside) like on the suv's or making a mount under or through the bumper or making a whole new off road style bumper and just incorporating the mount for it in it. I've put that project on hold until after I decide if I'm going to buy/build a truck camper or buy/build a trailer. If I go the truck camper route then I'll have to make sure any rear rack has enough clearance for it as they tend to hang back furthur usually sitting on the tailgate.