40 pounds should be fine. I have my pressure regulator set at 40 PSI.
I always use a pressure regulator just to be sure that my system isn't being over pressurized.
I just read in the FMCA magazine about how to test an RV water system. It said that the factory used to use 100 PSI to test for leaks in a new RV. Recently the pressure has been reduced to 80 PSI as a system check for leaks. It also warned that the test should only be preformed by qualified technicians as some check valves can be damaged if it is not done right.
Safe Travels.
JD