Propane vapor is only pressurized at like 40-50 psi in the tank, once it has made the phase change to a gas. This is probably pretty variable, too. That would be pretty low to regulate for using pneumatic automation.
The propane going through a phase change might lead to frosting, too, at high rates of fire- then again maybe not, since it is drawing so little to drive that piston.
I recall someone suggesting a 3.5 oz CO2 tank mounted in front to run the pneumatics. That seems like a good idea. It also defeats the purpose of using propane in the first place, since now someone would need to get CO2 filled.
