How many backflow protectors needed? Where?

[PA BAMBI II]

Looking to add a "city" water inlet to my trailer and have begun the process of thinking through what parts will be needed.

I understand the logic and safety factor afforded by backflow protectors such as this one from VTS:

https://www.vintagetrailersupply.com...-p/vts-725.htm

My question involves quantity and placement. VTS says these are often placed just inside the fresh water city inlet. I have also read they should be placed at the outlet of the 12V water pump so that city water cannot force its way through the pump and into the holding tank.

Others say that modern inlets and water pumps have built-in backflow protectionso an in-line options is not needed, but certainly one should be placed back at the hot water heater outlet.

I will add as many as needed, just confused on what that number is.

Thanks for any advice- Ben

[rmkrum]

Whatever backflow protection you use, make sure it is a check valve type, and not a vacuum breaker. Vacuum breakers have air vents, and they will leak at the worst possible time and place...