I'm nothing when it comes to electronics but wouldn't the exposed circuitry of the micro R/C will freeze under the cold conditions? Also, will the cold temperatures draw out more heat from the rechargable batteries? You might want to devise a "mini-blanket" for the snowmobit.
The snow accumulated on the Snowmobit has a good chance to melt so you should consider waterproofing the Snowmobit to prevent melted ice from finding the circuits.
Doubt that you can build it off a non-proportional micro R/C unless you do not want to worry about turning. Also, all that plowing the Snowmobit is going to make should be answered with more power; more cells and a high torque motor.
Anyways, good luck and keep updating us on your progress
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