[MrForbes]

Shop around for butt connectors that have sealing type shrink wrap outer skin...then you can just crimp and wave a heat gun over it and have a fairly reliable connection. Try a "real" auto parts store, or a full line electronics parts catalog or online store.

Being from Arizona I don't have as much experience with corrosion as the rust belt folks do...but you might try a round connector with a self closing cover, they are sold at "real" auto parts stores and trailer supply stores. Or get the small flat 4 wire molded connector, but get two of them, cut the wires off the extra halves and use them to cover up the connectors when the trailer is not being used.

A bit of grease over the connector terminals would help too, I imagine.