There is a metal plate on top of these but it doesn't address the 90% of the exposed rubber all around. A metal wrap could help though. Shrink wrap plastic could work as long as it doesn't age-out from the environment. I even thought of just bagging them but it would have to be serious stuff to hold up for years.

Something liquid/flowable/sprayable would get into the base where the metal and rubber meet. It would have to be flexible though and not petroleum based.