If correctly installed, the extend-a-stay adapter will be forward of the regulator, using the existing regulator to govern the pressure entering the coach.
I can grab a pic if you need it but I think you get it.
Been using it since I started full-timing- 3m now. I use the onboard for the fridge while traveling and a 20lb extend-a-stay for everything else. You'll like it that way
Works for me and could for you.
Take care and safe travels.