I have the Tire Minder system for both our MH and toad. For the toad, it uses an aluminum housing which does not effect the OEM TPMS. I am very happy with this setup with the exception of having to remove the sensors if storing the MH and or checking pressures with a gauge. I have found that when traveling and leaving the sensors attached, the need for checking pressures is no more than turning the system on prior to departure. Also, Tire Minder has a free battery replacement program whereas you send them the old ones and they send you new ones.
Yes, the system is expensive but IMO, I wouldn't travel without it.
Steve