Try to fit a Outerwear cover from
http://outerwearsracing.com/categories.asp?cat=11441
Dont know what would fit youre car best, but they have full covers for E-revo`s, Slash, Blitz and more.. My guess is that you will make one of these fit well, if you choose for a car that has approx the same shape on chassie.. If not, they sell big sheets too, for you to make youreself ;)
I run one on my E-revo now, and i dont get any snow or water in my chassie anymore.
Not saying its impossible that some snow gets there, but atleast it hasnt happened to me yet. And the best part, its VERY breathable..