Air density is problem # 1 at 3000 m and propane pressure is problem #2
#2 can be solved in a way that you work on the physics of the propane bottle: By loosing pressure, when propane gets out of the bottle, the bottle gets cold. Keeping it warm helps > plastic bottles are the worst in this direction, than steel, than aluminium. So an aluminium tank would help with the temp exchange to the environment.