Maybe 'cause I shoot the same camera at times, but prefer a different focal length, I have to say you've probably got one of the most durable set-ups for inclement weather. I think the sealed pentaprism gives an advantage over the F series for blowing conditions. Perhaps a different lube, with cold weather in mind, would give a slight advantage....but Tri-X would have plenty of lattitude to compensate for sluggish shutters.
As far as extra protection, perhaps a plastic bag taped to the UV filter would help ease your mind. My Nikkormat has survived years of outdoor shooting, including driving rain and snow during PJ football game work, with no ill affects. Have it CLA'd every few years and I'll bet you're OK. If you're worried, try a Nikonos with a 28, or a AF35AW (35mm FL, but slightly less expensive than the 'nos). The Action Touch is electronic, so I don't prefer it in the cold.
I think you've got a great set-up, and other than the bag, wouldn't do much besides keeping it in my parka during a blizzard.