Yep, a lot of the newer units do just fine with rubber stems. You have to remember that the original versions weren't designed for RVs, they were sold to Rvers, but, designed for the trucking industry. Much more robust valve stems on the big rigs. When RVers first started using them, the found out, real quick, that the civilian valve stems couldn't handle the weight of the truck transmitters.
Now that RVers are probably the biggest buyers of these units, they have been redesigned and made much lighter to increase their marketability; many folks might spring for them, but, wouldn't because all the tires would have to be taken off to have metal valve stems put on. Another issue with the originals, and again because of the harsh conditions that commercial trucks operate in, was that the batteries weren't user replaceable; they were sealed units for durability. RVers though, wanted the ability to change the batteries themselves to avoid the hassle and expense of swapping out entire transmitter assemblies.
The result? More and more of the units are "RVer Friendly", but, it is still "buyer beware"...read the description; there are still a lot of truck based units out there that are being sold for RV use. Read and heed the information you find on the seller's website, but, my recommendation is stay away from any unit that you can't swap your own batteries...they are going to be sealed and, as such, are probably truck based and will weigh enough that they ought to be on metal stems.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)