I bought the HD4 TPMS from Hawkshead because they have a patented "T-valve" so you can use regular sensors instead of having to use the flow-through type. The dash unit looks the same as a few others out there and who knows, maybe they're all made in the same plant..
T-valves and
tpms.caAvailable in the US from:
TVforMyRV.com This source has the better price for the HD4 package.
The T-valve is a new product and I had to buy them from the Canadian distributor separately.
A TPMS is highly recommended. There are a number of reasons why RV tires fail and this blog has some excellent info. from a tire expert and it's good to know what you can do to minimize the chance of failures.
http://www.rvtiresafety.com/search/label/Failure