Dielectric Waterproofing Grease;

Defend Your Connectors from Mother Nature
F-style connections are poorly designed and contain numerous air pockets which force a "breathing" of the connector with changes in ambient temperature. O-Rings, seal tapes, and brush-on overcoats are a great help but will not stop damp, humid air from creeping into your connectors and causing electrolytic (acid) failure.

You Gotta STUF It!
STUF (Silica Teflon Unionizing Filler) is an ultra-low density, all dielectric filler specifically formulated to simulate coaxial cable core that prevents moisture infiltration by occupation. It's been serving the communications industry since 1989. Simply mate a tube of STUF with connector cap end and fill. Then, thread the connector and snug it tight with a wrench. A slight resistance to tightening should be notes as STUF is channeled into voids. That's all there is to it!