I went the plastic tank route too, after reading CruxGNZ's write up some time ago.
The LS1 tanks ( this one's an '02 Camaro) fit the space nicely, aren't expensive, and are fairly simple to mount after fabbin' up some hangers.
I believe CruxGNZ's looked about the same, the tank's shape dictates what the mounts are gonna look like. I just made a cardboard pattern following the tank's angles and transferred it onto some plywood and made a jig out of it, to produce two identical pieces. The time consuming part is in mitering the metal.
For me, it was important to retain the tank's emissions function, to keep the stinky smells in the tank rather than in my garage.
I positioned the tank more to the passenger side to allow room for a single, drivers side, muffler.
The Camaro fill tube diameter fit perfectly, but to get a good, stock filler angle, it does angle into the trunk area.
Here's some pix:
Steve
The little round plate on the left is an aftermarket sending unit I added.
The straps came with the tank.