If you do some Internet searches on off-road accessories you can find the swing-away spare tire carriers WITH racks for 5 gallon gas cans on them. I've seen them mounted on almost every brand of SUV on the road. Some are designed just for carrying the gas cans and NO spare. They have steel plates to lock the cans to with a cable and can be covered with a tarp for concealment. One such supplier is JC Whitney - try this link as an example.