I ended up mounting a 5lb tank in a power tank bracket to the d-pillar of my 80 using the bolt and existing hole from the seatbelt hardware. My 3rd row is out, so the triangular piece where the seatbelt changes direction over your shoulder after it comes up from the floor was serving no purpose. Obviously a very stout bolt for safety reasons and that bracket it going nowhere. I have a swing out with a fold down stove table, and there was no way to mount the power tank bracket to that side of the truck without welding another piece onto the swing out. I keep an 8 foot propane hose coiled up in the spare tire and it’s a very clean an easy solution for my set up. Haters will say it’s dangerous to have a propane tank mounted at head level inside the cab, but it is locked down very securely in the bracket, and with an extra truck strap that I have added, it’s probably safer than most fire extinguishers you see riding around in that location.
I hope this spurs someone’s creativity.