Can PEX be used for the trunk
I have seen PEX used in this application. I also see PVC feed lines for Water supply in many jobs. As far as PEX, brands my differ a little, but the standard is 100psi at 180F
 160psi at 74F.  Most public water supplies range around 50 to 70 PSI, and this is cold water.  Check local codes, but I think you will be fine with proper connectors.