Geesh...I just pop mine in a jersey pocket, saddle bag, handlebar bag, or whatever is handiest for the bike I am riding. I don't worry about protecting it further from rain unless this thing they call a weather forecast indicates a fair chance of it doing so...and just a small sammich bag does the trick.
Cyclists seem to love over complicating things.
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey