When I'm connecting wires that are subject to outdoor exposure I'll solder them then coat thoroughly with a silicone sealant and use shrink tubing over that before the sealant sets. (From personal experience......ALWAYS slip the shrink tubing on to the wire before soldering!) The silicone is to slow down the corrosion inside the wire insulation as water always seems to find it's way inside.
I am going to solder then use shrink tubing. Another question: Is there a way to test my brakes to see if they are working while my RV is parked?