Solder everything. I grew up with this mandate from my Dad. Use Rosin core, NOT acid core.
Got this off the web:
Rosin core solder contains rosin, which is usually a purified pine tree sap, as a fluxing agent. The flux can be inactive, in which case it simply covers the area being soldered during the process (to keep oxides from forming), active or mildly active , in which case it will remove light-to-medium oxides that were present before the soldering process began, or highly active, which will remove almost any oxide or stain on the part and allow a good solder joint to be made.
Crimp & Glue Lined Heat Shrink. Solder connections are not ideal in boats. You create a solid section connected to a flexible section. Over time this can create stress & break at the solder connection.
Solder, and heat shrink only.... I solder everything, even up to the speaker wires.. I've had my share of nav lights flickering, and b.s. not working.. And, i'm cheap as hell... It takes a little longer to solder, but much cheaper, and you always have a solid connection..
Normally I would say solder and heat-shrink everything, and silicone. However, I've been on an SKA Fishing team for the past 3 years, and since I was the one with a degree in electronics engineering, I was tasked with keeping everything working. We've went through dozens of pumps in single year..
I've had to rig up some stuff during a tounament to keep things running, and discovered something kinda cool, you may want to try if you're in a pinch. I ran out of crimps one day and only had heat-shrink and 5200. I twisted the wires together, slathered them in 5200, and ran the shrink over it. Those connections have faired better than the crimped/shrinked ones. They are most assuredly watertight, since the heat shrink pushes the 5200 out and creates a pretty good cocoon.
It's not a very strong connection, but one that will not fail due to corrosion if underwater or in a bilge.