I used weatherstripping adhesive, (the black 3M stuff) I think mine was about the same as you describe, but I didn't cut or modify mine at all. I applied the adhesive, and you have to kind of "squish" the gasket together and stick it down. It will work. The adhesive, if used properly, will bond instantly so you don't have to worry about the gasket sliding around and pushing up or wrinkling. Once you get it stuck down, close the cowl vent and leave it closed for a day or two until the adhesive cures completely. You'll do fine.
