I have seen people use a shower cap to keep the esc and motor dry. Since the MGM ESC's run cool, you could probably cover it without having heat issues.
If you get the hydro version (sold here at rc-monster store) which are waterproof coated, you should be ok unless you are stuffing the ESC full of snow (then cover the ends).
soon as I enter the house from the cold... I put the electronics part of the RC toys right in front of a small electric heater, to prevent condensation
I already have a new e-maxx on order at my local hobbyshop
Bur i don't think the stock setup will be enough for me so i'm thinking of upgrading to brushless rightaway