It's important to get the water out first or it will keep freezing and likely fracturing the brittle cured epoxy. Hayden's use of a vacuum pump to lower vapor pressure is a good solution along with some hot sun beating down on it for heat. Vacuum bagging works well with prepreg and a curing oven. This is more like using an enclosed mold and using a vacuum on one end and a resin reservoir on the other end. It will be heavy and ideally a lightening mixture added to the resin that is also waterproof will get some weight out but you also need low viscosity to flow and wet out the core.