Living on the Coast is great! Cool, moist, and that fresh salt air coming onshore after thousands of miles of open sea. Pleasant in the nostrils but tough on your antennas. Put a bare copper wire outside and it turns green almost immediately. If you are inland a ways it's another story, the wire is still bright and shiny for years. Ah, well.
That corrosion causes all sorts of problems. Not just the long-term destruction of the wire but almost immediate intermittent connections, increased intermodulation products, and generally degraded antenna performance. Copper oxide is a semiconductor, working as several distributed and sloppy diodes. They act as frequency mixers and multipliers, turning your antenna connections into a mess of unpredictable spurious signal product generators. Even strong incoming signals mix with other signals to produce puzzling interference.
When moisture gets into your coaxial transmission line it's even worse. If the dielectric absorbs moisture then loss increases and your signal decreases. That low loss foam loses its advantage when it becomes a sponge. That nice and shiny braided shield becomes a wick for moisture and spreads it down the cable, turning it first to green and finally to black as water eats its way into the metal. Soon your low-loss coaxial cable is just a long attenuator.
What do we do? Two choices: Keep it dry by keeping it indoors or sealed up tightly, or use corrosion resistant components.
If we use stainless steel antenna wire then the system efficiency is a bit lower (due to higher wire resistance) but the wire lasts for many years. I have employed used salmon trolling line (about AWG #16 ?) successfully. At one time I had a quarter mile wire strung over saltwater as an antenna. Fifty years later I am still using pieces of the same wire. No sign of corrosion yet. It is hard to work with and you must use compression clamps for connections.
If you use insulated wire it will keep the elements away from the copper for a while. The insulation effects on electrical performance are minimal. The insulation just adds weight and, unfortunately, no one makes copper jacketed steel antenna wire that is insulated. So plan on leaving slack in it and put up with the sag.
That leaves the outdoor termination connections to be dealt with. Weather proof connectors are few and far between. They involve lots of gaskets and “O” rings to seal them. Even then, they should be protected from the elements. Avoid putting connectors outdoors if you can. Use solder or clamps and do your best to protect them. PL259s are not weather resistant. “N” fittings and BNCs are not much better. Wrap them and put them in a dry enclosure.
The new silicone tape looks promising but has only been on the market for a few years. I'm waiting to see how it holds up before recommending it. For 50 years the standard in weather resistant tape has been 2 layers of rubber splicing tape covered with a couple layers Scotch(tm) #88 vinyl tape and sealed liberally with Scotch-Seal(tm). However multiple coats of “Liquid Tape” like Performix(tm) LT14023 or Permatex(tm) 85120 will make an easy-to-apply flexible coating for any exposed connections.
Flooding the connection with silicone grease before taping helps exclude water. The grease is a good dielectric and does not affect performance, but talk about messy! Hard to re-work, too. I have heard of using hot-melt glue to seal connections but I doubt that it would bond tightly nor remain flexible enough. Silicone grease flooded heat-shrink tubing is used in underground electrical work and might be worth consideration.
Housing the connection should be carefully considered. An inverted can will help. Be sure to leave the bottom open so that no moisture collects. Likewise, if you enclose your coax in conduits be sure to slope each run and provide drains so no moisture collects for long. Those plastic electrical boxes are nice, gaskets and everything.
For top-notch station performance check your antenna system frequently and replace any corroded or degraded components.
de ND6T