The smaller BMW style ones are better as the contacts are stepped so the plug can't move as easily in the socket. They also have the rubber bung that makes them splash proof. John Deere use them in tractors and sell at much better prices than anywhere bike related if you live anywhere agricultural enough to have a dealer.

As far as waterproofing electrics go, in my experience (winter testing trucks is a good place to learn) you need to make a decision. Either keep water out or let it pass through. The worst thing is to use PVC tape or poor connectors that'll allow pools. So:

Keep it out 1: solder the wires onto the connectors even if they have crimps or screws then heat shrink PVC over the top.

Keep it out 2: IP68 connectors. The IP number tells you how well they keep out dust and water. The rubber seals in IP68's need to be fitted correctly, but do work. I have three of these (GPS, heated jacket, heated visor) on the bars instead of the BMW type plugs and they survive as QD's for about three years at a time.

Let it through: Open plastic cage type connectors with 6.8mm crimp on brass spades rot in about 2 years, but are so big it doesn't matter. Mount them so the water passes through and they work.

The BMW type acessory plugs can be a water trap. I'd solder the wires on, heat shrink and drill a 2mm drain hole.

Andy