Sensors are unreliable....your best bet is to learn how often you need to fill propane, when the holding tanks need to be emptied or freshwater tank filled...as you camp in the MH you will get a sense for how often these tasks are needed.
For propane tanks, some RVers tap on the tank, pour hot water on the tank or weigh the tank to determine the level. I just lift my tank to feel the weight, a light tank is near empty a heavy tank is full.