One of my first RVs had a Marshall regulator With the first and second stages separated by a quarter inch pipe nipple. I replaced that nipple with a tee, gas shut off valve and a 25 foot hose with the male GCA 600 connector on the end. I have 18 psi after the first stage and that is plenty of pressure to run any of the LP grills and cookers that use the disposable cylinders and their own regulator. I move that regulator from RV to RV and I will never part with it.
I think Rego still makes a LP regulator with automatic changeover and a pipe nipple in between the first and second stages so if a person wanted to get one of them they could do what I did. Craig
