After I solder the leads to the switch terminals I coat the switch casing with liquid electrical tape. The only thing that I don't cover is the toggle switch and the threads. I usually use a couple of coats and let it dry completely before installing. I put a very thin film of di-electric grease on the switch and threads then install the rubber boot. I'll usually put a thick bead of Marine Goop around the base of the switch to cover the threads. I've had switches last for over 3 years with no sign of corrosion using this method. A little extreme, but it sure does keep the electronics in good working order.

We actually fill the boot on the switch with Dielectric grease. Switches will last a long time. All Wiring is Marine Grade all the way down the the Shrink tube.

I tried filling the boot with di-electric grease. I found that it would migrate inside the switch and foul the contacts. You could clean the contacts somewhat by cycling the switch numerous times, but it really wasn't an ideal solution.