Step 1: Label freezer bag
Acquire a box of heavy-duty quart freezer bags. You want to be able to thaw the tomatoes in one-use shots, so don't go for bigger bags unless you're into seriously large-scale cooking.
Label and date the bag with a waterproof marker before you get started, then flip the top inside out to avoid getting goo in the zipper opening. Cook's Illustrated says that regular zip bags work better than the ones with slide closures, and the thicker the bag the better. Thicker bags block evaporation better, while bags don't seal properly directly under the slider.
*It's very important to label and date your freezer bag. Years from now, when your grandchildren chisel this out from under layers of ice, they'll want to know whether this bundle requires special hazardous waste disposal. It will also save costly carbon-dating.