"Best" way to weather proof 12 volt elec connection

ScottG wrote:
Regular heat shrink isn't water tight. For that you need the type that has glue inside which you can get at marine supply places. Or, you can smear the inside with silicone and then shrink it up.

Man things just trap moisture and become counterproductive. The above suggestion is excellent.

Dieelectic grease is a good thing too because it does not trap water. Try to mount in such a way that water will drain away and not to the device. We call that a drip loop.