TPMS is a great investment IMHO.
You'll need to be more specific on your dual set up. Do you have a "Cats Eye" type of set up which connects both valve stems to a single filler stem and balances the PSI between the two tires? Are you sure the two are connected together or is the stem for your inner dual just not accessible?
I've often wondered if a TPMS would work on a set up designed to balance the PSI on duals. My understanding is that a "Cats Eye" type of balancing device will close off one of the tires if it senses a rapid loss of pressure to avoid causing both duals to go flat. If that's the case I don't see how using a single TPMS sensor on the single valve stem would do much good.
Hopefully we'll hear from someone who has tackled this.
Rick, Nancy, Peanut & Lola our Westie Dogs & Bailey the Sheltie.
2007 Itasca Ellipse 40FD