Steve...
It looks like Marty's birdcage is made of aluminum, so corrosion where the connector is bolted shouldn't be a problem.
But if that's a concern, a little clear silicone caulk should seal it up.
I was specifically referring to covering and protecting the "guts" of the female SO-239 bulkhead connector.
Those little plastic caps will keep the inside of the bulkhead connector nice and shiny. But, as I write this, I
occurs to me that a little squirt of Pro-Gold every now and then wouldn't hurt either.
73 de ND8L/4/FNG