One nice option, at least if you aren't going to be disconnecting and reconnecting this zillions of times, are Weather-Pack connectors, such as
this one. They're good quality and relatively affordable. You do need a specialized
crimp tool to install them. (I think there are compatible, or at least claimed-to-be-compatible, crimpers available elsewhere for less money; the same might be true for the connector kit as well. I'm not affiliated with All Electronics beyond being a satisfied occasional customer.)