Al,
This sounds like a pretty good leak, as Steve stated you should be able to hear it. Park the coach on level ground chock the wheels, parking brake off, build up pressure until compressor cuts out and then shut the motor off get out and listen for air leaking from the front or rear. The Maxi parking brake should auto apply around 50 psig. The suspension should stay up as the air is locked in by the system. At the stated leak rate you should be able to hear it, if not its time for the spray bottle and dish soap.