[Ironhorse]

Not sure about the " aux " tank portion but I removed my in cab tank from behind the seat and installed a poly tank from GMC Paul's. Did it several years ago and glad I did. Gives me some more storage room behind the seat and I was able to use the corner speaker mounts that bigblock73, (board member and nice guy all around) fabed. I have them installed now but not hooked up. If you would like I could take some pics in a day or two of my rear tank set-up and give a brief how-to, at least the way I did it anyway. Took very little welding skills of which I have none or the welder either.