Many RV manufactures use a combination City Water inlet/Pressure regulator made by Sur-Flo (I think it is, hold on I'll check, one on the shelf in front of me)
SHURflo (mispelled it) A Watts subsidary.
I DO NOT recommend these.. Oh the regulator is ok, I give it a 9 and I have the inline version of it..
The proper place for the regulator is on the park water spigot,,, THEN the hose.. Here is why
Just outside my window (Behind me) is the park water faucet.. pressure there has been measured at over 110 PSI,, High enough to blow the ends off my fresh water hose.. Hooked to it is a ZURIN 3/4 inch adjustable regulator,, THEN the hose,, 50 PSI.. Zurin is brand new.
WATTS makes one that is much like the Zurin,, I have one of those too but it's old and in need of a rebuld.. Both of these if I turn on the outside shower while watching the gauge,,, The pressure needle (50 psi side) well on the Zurin it remained frozen in place, does not move,, Same with the Watts when new but due to the ravages of age. As i said it needs a rebuld..
By the way I give these a resounding 10 on a scale of 10. FULL FLOW at 50 PSI.
The SHURflow needs a kit too It goes way down now days.