I installed a small universal heater from Vintage Air but I have not tried it yet. I did not like the complicated vacuum-activated water valve and have installed a manual valve in the water hose in front of the firewall. Your fabricated unit looks GREAT! Nice Work! The Vintage Air unit mounts to any flat surface with two bolts and I hung it on the inside of the firewall. Your under-seat position probably avoids the problem of routing hoses through the firewall and can be under the floor. As of now the space under my seat is wasted but I have been thinking of some sort of wooden drawers with space for maps and small tools under there. In my case I mounted the outlet where my wife's feet would/will be, a real consideration, although she wants air conditioning which I refuse to do considering the many leaks around the windshield and wind wings!

Don Shillady
Retired Scientist/teen rodder