I agree with Tireman9 that any Big Rig should have a TPM . . .as it will save a lot of pre-trip tire pressure testing and give you the piece of mind that you WILL be informed . . . in real time when any of your tires start to leak or get punctured.
According to the experts, tires always lose pressure FIRST, before they get hot and blow out/explode. The TST gives you warning when any tire falls below the pressure limit that you set. It gives you a margin of "time" to slow down, pull over while you tires are still on their rims. ALL of the bad tales you hear about tires blowing with debris going into the bedroom/coach are due to the Driver not knowing that the tire has become overheated . .. due to loss of pressure. He finds out when it ruptures and . . . if it comes OFF the front rim, you are in a world of hurt!
Our 38' SAFARI has the TST 510RV Tire Monitor System with sensors on all 6 tires. The monitor can handle up to 18 separate tire sensors, in case you have a Toad - those tires can be monitored too. The newer TST 507RV system has user replaceable batteries for the individual tire sensors, which is probably what I would buy today.
I never leave home without it being turned ON. . . and no I am not a TST employee.