The inlet connection is also a water pressure regulator, no need for another.
The campground connection has an anti-reverse flow valve on it, expansion in the hose from the sun and heat of the day will flow into your Airstream. That excessive pressure if any, as well as expansion in the water system from the gas/propane water heater, will be taken by the air bubble in your water heater (that's how they are designed, believe it or not). That air bubble must be maintained or water will leak out the water heater temp/pressure relief valve, may find a weak connection in the plumbing to leak, and may over stress the connection hose or connection.
The hot water heater bubble is frequently lost. We added a backup by simply putting a water pressure accumulator in the cold water plumbing line that goes to our bath sink. Camping World and Amazon has them.
Doug and Cheryl
2012 FC RB, Michelin 16, ProPride 1400
2016 Ram 1500 Laramie Crew Cab 4X4 Ecodiesel 3.92 axles
The Truth is More Important Than the Facts