Watch storage/humidity

I don't know if this has been covered in the past, but I'd like some input on this. We all know that humidity and condensation is the main enemy (along with dust), but what is the optimum humidity level percent when watches are in storage?

This much I do know: coins should be stored at less than 37% humidity, stamps 50-55% humidity (according to Stanley Gibbons and the National Postal Museum), but I want to know what the optimum humidity level is for watches.

Yes, I know, this is just one more thing to drive us nuts, but not sure if you guys are as neurotic as I am, do you use silica, a hygrometer, etc. I use prosorb 50% humidity stabilizer for stamps, and eva dry for coins, but what's proper for watches? Thanks!