Here is your solution, Coastal can build custom insulated boxes for your whole house fan. The top is removable, so when spring comes along, just jump up there and pop the lid off and you are good to go. 
Is your whole house fan abandoned? Do not want to replace sheetrock and paint at this time? No problem we can build this custom whole house fan cover for you as well.
This not only stops air flow from escaping your living space, it acts as a dam to keep your newly installed cellulose in tact!!!