Cool, just trying to help out.
I know working up under my XJ this past weekend, there is just not a ton of room to put a second tank unless it's really small. I would definitely not put it inside unless you have some way to seal it from the rest of the interior. Don't want any possible leaks or vapors to be inside.
As for your idea of a transfer pump, that would work fine. I think Scott did that on his Toyota and I have read of a few others doing that. The hard part is figuring out the second tank mounting and filling.
Good luck with coming up with something and share pics if you do.
