Well it can be done. Ive experimented with two tanks on one of my bikes which was a norco bush pilot. I had a 2.5 litre main tank and a 990 mililiter reserve emergancy tank mounted just under the seat which increased my range an extra 20 k.m. I have a few pics of it here. Each tank had it's own seperate shut off fuel valve and the rear tank had a inline fuel filter on it because it didn't have a built in one where the line attached to.The rear tank was off of a lawn mower that was being throwen out in the garbage and it's made out of plastic.Luckly it still had it's fuel cap still on it when i recovered it.