Splicing into existing wiring

What are ya'll doing to splice into existing wiring to add lights, or anything outside of the cabin? I want to add another Perko light under my stern seating, and put a light on the swim platform, so i can easily splice into existing wiring in the transom locker. My concern is with the locker being a wet muggy area since its outside of the camper cover. For low voltage 12v, should i just snip, twist the 3 wires together, tin with solder, and then heat shrink to seal? I figure any mechanical connections such as T's, or crimps, would be prone to corrosion.

Snip and use an adhesive lined heat shrink butt splice to connect.

Or solder and use sealant lined shrink tubing

Bill Curtis said:

Or solder and use sealant lined shrink tubing

Click to expand...

Didnt realize that existed, and see they have sets available at harbor freight. Now i know where i'm going. Thanks