Ok. So I've been working on my 82 Sierra and today dropped the gas tank and replaced the fuel sending unit. Got everything put back together and got to wondering something. The truck originally came with dual tanks but the p.o apparantly put a different bed on at some point and did away with the passenger side tank, why I don't know but the selector switch was still mounted to the frame and I could see where the old tank was mounted. But the bed has only the driver side fuel door. That leaves me with one 16 gallon tank and with a four wheel drive powered by a 350 I ain't gonna go far between fill ups. How do fuel cells work? If I were to mount an extra tank in the bed would it work by gravity feed? I know I could put a tank where the spare tire goes but I'd guess a spare in the bed would be cheaper and easier. What would I need to do to get it hooked up and working and is it really feasible? I wouldn't really be concerned with being able to tell how full it is, mainly just use it for a spare on longer trips than just around town.