"The only other thing I can think of is that the salt might affect the solder in some way, but I doubt that is true since it is mostly lead."
You've been misinformed. Electrical solder *was* usually a tin/lead mix 60/40 ratio, so it was only 40% lead. But lead has been discouraged and often banned for quite a while now, lead-free solder has become the norm. So yes, there are galvanic effects and corrosion possible between the wire and the solder and the fittings.
On the other hand, NASA and the USAF use solder-filled fittings made by 3M for wiring that goes up up up. The fittings are soldered by heat gun or IR gun and they shrink-fit over the wires, the solder comes from internal rings in the shrink sleeve. The fittings are waterproof and gas (atmosphere) proof when properly made. But, those aren't cheap fittings. :-)