I waterproofed my lipo with a couple coats of liquid electrical tape. I put it around the seam, where the leads leave the case, and on the backside of the connector. She has been covered in snow, splashed through puddles, and even accidentally submarined on a few occasions with no issues.
I have some of that corrosion x sitting here for another project but have not tried it yet. Other people are certainly getting good results with it; check this out: