You can use a LP tank you just need to be safe and fill it with water and dish soap and let it sit over night and repeat 2 more times. DO NOT use a fuel oil tank as you will never burn off all residue in the tank and the last think you want to do is make somebody sick from your food. Aother Great choice instead of a LP tank is a Air Compressor tank. You need to know what you want (Offset, offset reverse flow ect...) when cutting your doors out of the tank dont do it all at once so you dont warp the steel, cut the majority of it but leave the corners uncut and 2 spots in the middle on the top and bottom. and plan ahead so you dont have to do it twice if you want pics or have questions feel free to e mail me or go here: http://www.barbecuenews.com/forum/default.asp?CAT_ID=3
Talk to the local LP company first and get their take on it. I feel confident they'll disagree with the water procedure. Lp tanks are round anyway which reduces cooking surface. use an oval oil tank(new if you prefer). We made one out of a used oil tank and had no effect on taste or health.