I had actually done the gravel thing 35 years ago with a motorcycle tank. I put them in the tank and put the tank in my wife's clothes dryer w/o heat and stuffed pillows around it to secure it. It turned out GREAT. Thought a variation of that might be worthy for the truck.
Lots of good ideas and advice above. Thanks folks. I'll let you know what I do. If I build the rotissorie, I'll take some pics for ya.
