If you decide to get one, aluminum is the way to go. I put a plastic fuel cell in a 68 Mustang for a man who was concerned about safety when his toddler daughter was riding in the car, and we had to go back in and redesign things. The tank would warp in hot weather, so we ended up fabricating a sheet metal box to support it. Fuel capacity isn't a problem as long as you've got enough room to mount a big enough tank.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!