Aftermarket gas tank?

Ah, and here I was thinking the opposite: cut that spare tire well about 3 inches deeper to fit a decent tire, and take it out of the tank. I mean, how many people use their cars for long road trips? Oh... well, there's me, I guess. Maybe not a good idea.
LOL... Maybe I could do that so I can fit a rear and a front in the spare tire area...turn it to 9 gallon tank