Width of trunk?

Im shopping around for a 97-98 carlo and Im about to build a subwoofer box and I need to make sure the box is going to fit in the trunk. The box is going to be 36" wide 15" tall and 20.5" deep. Could anyone give me the dimensions to make sure this would fit? I really dont want to build another box in a month. Thanks for all the help in advance. Aphix.