FWIW, my 60C and 2720 have both been on the bike through very severe rain without a problem. I am shocked if the Montana is not as waterproof as they are.
ETA: I just checked on the Garmin site and they are both rated at IPX7.
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2005 R1200GS | 2013 R11200GSW | SOHC4 208 | DoD 2032 | BMWMOA | BMWRA | YB
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