Our TPMS choices reflect the customers' desire. Our equipment goes into Newmar coaches--they use Valor TPMS via RV-C bus. This is a good internal sensor. Spendy--and don't ask me how much; you'd have better accuracy looking from the consumer-side than my OEM info.
This is the extent of my knowledge of internal sensors. SmarTire was good (and still is) --though the units are out of production. The sensors are easily enough gotten via Dickman tire in Junction city.
Otherwise, internal type notwithstanding, we've partnered with PressurePro and TST for screw-on types. The latter is a pretty good set up which uses the flow-through sensors. Its also being incorporated into v5 VMSpc.