I don't know the specifics but sounds like you have wires you are attaching together with various methods and they are not reliable. Solder and heat shrink is the answer. Adhesive lined heat shrink is even better. If you do not want to mess with soldering, a reasonable alternative are solder seal connectors like these
https://www.amazon.com/120PCS-Solder.../dp/B07S62KYSL
I picked that brand and link at random. I've used the same on exposed trailer lighting for years and much better than anything I've used other than soldering and heat shrink manually. Just my 0.02 with them.. I have better luck using those connectors with an actual heat gun vs a pocket lighter or a micro butane torch with a heat deflector tip. I think the later two get things too hot too fast.
If you are dealing with jacks and plugs you are trying to seal and not wires, strategic placement of dielectric grease around the connector may help.