+1 what Greywolf said.
I never did find one that looked entirely waterproof while in use. But it really doesn't matter too much, for the reasons above.IMO.
This is what I got, with a matching socket from the same supplier, they click together and allow
very little water in while in use (I plug my car sat-nav in, and no problems in some truly torrential rain). More water gets in when I wash the bike, just a matter of a quick dry with a cloth after.