I use a 10",1 micron carbon block filter, in a single stage housing. The filter is mounted in the one stop service compartment in the rear of the trailer. This allows accessibility for changing the filter which I do once a year. It is plumbed from the outlet side of the pump and would filter all water coming from the on board storage tank.
In addition to that, I carry a second filter and housing that has been set up with a pressure regulator and hose fittings and I use this when I am using city water. This screws on at the park water faucet and your water hose connects it and the trailer. This setup protects both your hose and trailer from being over-pressured and takes the chlorine and particulates out of the park water.
1964 Overlander/2000 f250 Crew Cab 4X4 PS WBCCI# 5600