RVGUARD RV Water Pressure Regulator Valve, CSA Approved, Lead-Free Brass Adjustable Water Pressure Reducer with Gauge and Inlet Screen Filter for RV Camper Travel Trailer

You need one of these. https://a.co/d/0dQQsJet Somewhere between the spigot and the RV. I'm not going to open that can o' worms again.

I would do one of the brass-bodied pressure reducers with a gauge (example) directly on the hose bib, then the timer hung directly off the outlet of the PRV, and hose from there. If the house's water pressure is above like 100psi then I definitely wouldn't leave any plastic things connected at full pressure.