The aerosol sound deadner would not be a good sealant IMHO. Liquid nails along the seams should be all you need. If you have a speaker "cup" (terminal box on an enclosure) those leak very often, you may want to double check it has a gasket around it. Window weather stripping works great (1/4") Use that on your subs mounting lip as well if you do not have a carpted mounting surface.
95 Contour SE '01 3L 
