^^^ The pressure regulator on the shore tie hose? YES. I think the brass ones are better than the plastic ones, but I had a brass one shut the supply off.
"fitting entering RV" - Where the shore tie hose attaches to the coach? There's a check valve in it. If that's what you worked on, did you get it right?
We've had two Class C's and the water systems were different. First had a shore tie connection and a separate "gravity fill" where we just stuck a hose into an opening, like filling a gas tank. Current one has only the shore tie and valves inside have to be worked to fill the tank.
If you're taking parts off the outside of the coach, be sure they're sealed in place when you're all done.