I don't think regular aquarium methods would work. What I would do is build a enclosure from floor to ceiling with wood studs, sheetrock and insulation. Install and electric space heater at the bottom, this with typical aquarium heaters should keep the tank heated. Any doors or access panels would also need to be insulated. An insulated door or panel that could be place in front of the tank when not veiwing would help retain the heat also.
You would need to install an exhaust fan on the enclosure for the summer though in case the temp got to high.
As a note, last winter I got a 120g tank and wanted to test for leaks. I placed it in my garage added water and 450watts of heaters. Temp outside was in the 20s and the water in the aquarium had a thin layer of ice on it.