If your going fenderless, you might want to consider the trunk. I built mine to go between the trunk area and the back of the seat, standing up (holds 18 gals.) Fumes aren't a problem if you vent to the outside. I open trunk lid to fill up, but you can have a fuel door on the outside if you want. If you have fenders some people put tanks behind the running board splash aprons.
What ever you do, don't put the dual tanks under the car. I have those and when you go to the gas station you fill one side up then have to move the car so the hose will reach the other side. More trouble than it is worth.
Never, Never put a gas tank inside the passenger compartment without enclosing it in a firewall first. No matter where the thing vents by your design, it just may vent into your living space too. Just light a smoke ? BOOOOMMMMM!
Rock Valley Antique Auto Parts in Stillman Valley IL makes a stainless tank that mounts at the rea of the car similar to a 32 Ford. Then there are those saddle tanks under the runningboard aprons.