If future disconnection is not required then crimp type butt connectors can be used.

I favor the heat activated butt connectors which internally self solder the joint and have heat activated adhesive sealant which seals the insulation to the connector shell. Waterproof, reliable wire connections. I use these on marine wiring which requires high tolerance to moisture and corrosion.

Careful use of a lighter or compact flame torch makes quick work of heating and sealing the connection after crimping.

This is the solder and seal version

These are heat sealed but do not have the self solder feature.