So far the best I've seen is connectors held on a vice, molten solder poured in, the wires added (while the connector is still heated), then the connector crimped by a tool which does two crimps.. Once it cools down, the excess solder is removed and heat shrink tubing is brought over the connector and put into place.
I'd probably just go the route of using a good connector (one that isn't open-ended), a decent crimp tool, and then maybe even using Plasti-dip to dunk the entire thing and then scrape off the plastic on the electrical contact surfaces. There is still oxygen in the connector, but solder has a nasty habit of breaking if exposed to vibration.
