Auxiliary Gas Tanks?

[RMBLFSH]

Hi All.
I am new to the forum and '67-'72 Chevy trucks.

I recently purchased a '72 Cheyenne 1/2 ton, long-bed 4x4, that has the gas tank located in the cab behind the seat.
I would like to add fuel capacity.

I'd rather not cut holes in the bed sides as the truck is pretty straight, I'd like to keep the spare tire where it is, and don't want a tank taking up precious cargo space in the bed.

I am not too concerned with originality, and I'm not really interested in cobbling together something from used parts.

So...is there a place that sells complete auxiliary fuel tack systems for these trucks that meets the criteria I have outlined?

I realize I am being pretty particular, but this is more of a want than a need, so I am willing to live without if I can't find what I want.

Thanks in advance for any help.

Rich