veloglider

i am gonna build a box sealed and i have just purchased a used 15" mag off a guy for a good price. i want the volume to be 2.5 cubes and have figured out the size i want to accomidate it in my chrysler 300 trunk. the measuremants will be L 24" H 18" and W 10" which comes to exactly 2.5 cubes and i want to know is the width of 10" enough since it requires a mounting depth of 8 1/8"?