enclosure?

Should I use expanding foam instead? I have to seal 2 small enclosures that lead from the car's cabin to the trunk. They are very small about .75 cubic foot . I've stuffed the crevices as much as I could with acoustic fiber and polyfiber. (am try to stay away from expanding foam since it makes such a mess).

However, I don't know how well a job the fibers will do for sealing against pressure generated by 8" woofers.