Why Coax relies on a clean, dry dielectric between the center conductor and the shield. When water wicks in through a cracked jacket or an unsealed connector, it soaks the dielectric and braid, raising loss dramatically and corroding the shield, and the damage spreads along the cable. That is why outdoor connectors should be sealed with weatherproofing tape or sealant.
Watch out Solder flux is a concern for cold or corroded joints in connectors, but it is not the classic cable-killer; and coax does not care about how fast transmitter power varies or about long key-down operation as long as its power rating is not exceeded.
Water is coax's worst enemy: seal every outdoor connector.