Tire Pressure Monitors
I've had mine at least 3 years and haven't had any problems with the O-rings so far. The wheels are covered 3 months of the year, but the trailer is used regularly the other 9 and this part of Texas gets more than its share of sun and heat and the sensors remain on year round. That is a good tip to look at them at least when replacing the batteries. Did you get the replacements from a local hardware store or the TPM vendor? They could be neoprene, nitrile, silicone or one of any other compounds designed for particular applications. Some may be better suited for exposure. You would think the vendor would provide rings that are appropriate.
Air Safe Hitch, Reese Dual Cam 800#, Centramatics