When you say "weather proof" - do you mean rain, snow, or both?

For rain, a lot of people seem to feel that simply installing the Koolstop Salmon pads has increased their wet weather braking performance to around the same range as disc brakes.

And again, if it's just rain you're worried about I don't think that getting an IGH with a chain is going to make any difference whatsoever. Rain mostly effects the chain, and if you still have a chain...well, that's that. I haven't done an intensive comparison or anything, but I do own a bike with an Alfine IGH and I don't know that's it's any better suited for rain than my derailler bikes.

If you want the ultimate in low maintenance, it seems like IGH+Belt Drive is the way to go - you get rid of all that chain maintenance stuff. But they're not cheap, and require a special frame (frame needs to be able to come apart in the back to replace the belt or get the rear wheel off).