Even with a top on Chicago get's rather cold...-10 when factoring the wind chill. My old zook had slant back top that made wonders with the heat. adding this curtain to the full top would allow me to keep the enclosed storage in back and still be warm in the winter!!
should work fine mine was quite a bit warmer than the full top my heater works really well too though i took the heater core out and fully cleaned it about a year ago.