You'd be better off getting a basic double-walled three season tent to use year-round (something that could be 'closed up' in storms/ opened up for ventilation on warm sun-shiney days), and adjusting your sleeping bag system. Either have two sleeping bags (winter-weight and a summer bag), or one sleeping bag that has enough room in it so you can wear your insulated clothes while in it at night in the winter. I used to camp quite a bit in both winter and summer, and both sleeping bag systems worked well for me. Just my two-cents worth of experience.