I think crawford is askin for the same thing i'm thinkin' about... an "under the bed" tank", which you guys aren't talkin'about. I've looked at aero as well, but I have a short bed and would still like at least a 60 gallon capacity. I'm not really interested in an R&R bed tank and want it to be permanent as well.
My only comment to crawford is... doin' it right means not drilling the frame... aside from that, I expect it's gonna be a shade pricey, so it better bump up the capacity to where I need it. There was one other company putting together an aftermarket tank, but they e-mailed me and said it wasn't approved yet, and when it was, was only going to be 54 gallons total. Not really worth 800 bucks in my book.