Speaking of a JetCat only.

If you want to take the propane offboard, and cut the line that feeds into the shutoff valve. Install a one way shutoff in that cut line (that stays with the offboard part). So the tank, filter, etc all stay offboard, the shutoff valve stays onboard.

The shutoff valve keeps any gas from traveling out of the turbine.

This saves maybe 1 ounce of onboard weight, maybe 2, if you use the gas dump feature of the JetCat.

If you delete the shutoff valve, then you will need a checkvalve onboard, and you will have to manually throttle the gas offboard and try to stay in sync with the startup sequence.