I go with Dave -- better to use salt. But why wait until it warms up? I saw some stuff in the local hardware store that says it's effective down to 5-degrees.

Also -- if your scupper lines have any s-curves that trap water, you might want to consider they will clog with ice too. Be careful about chopping or ice picks, easy to damage the fiberglass.

I'd suggest that until you can get it covered you should go after every snowfall and shovel the cockpit. I have found that a children's snow shovel is ideal on the boat -- it's smaller and the blade has a poly-plastic edge not likely to damage the fiberglass.