Woofer fires directly into "board"

[eRiCdWoNg]

Just wondering if Im going to have any problem before I finish building this enclosure. Basically its for my car, a 98 Covette. The bottom of the enclosure is fiberglass, molded to fit the contours of the rear most storage well and to save some weight. It is approx 2.5 cubic foot (before driver displacement and port). The top of the enclosure will be MDF, so I dont have to mess with trying to smooth it out and get nice angles. Anyhow, my concern is when the top of my car is off and stowed in the rear, the woofer will be firing DIRECTLY into this board, with maybe 1/2" of clearance between the cone and the top. I really do not forsee anyway around this. I've tried a woofer enclosure in the middle of the car before, and when the top is off theres no "loading" from the car and it creates a really wierd out of phase response right at the crossover frequency.

I'm still exploring all possibilities, but this will be a ported enclosure and I'm thinking of firing the ports from the sides. Any suggesions when there is limited clearance like this?