Re: Rough Volume of Rear Speaker Enclosure?
One other consideration is excursion and how much clearance there is between the enclosure and the panel. I can't think of a good way to check this off the top of my head. You may be limited to a flush mount setup cutting into the net volume further.
Just to give you another option, Kicker has a 6.75" shallow mount that may fit. Depth is 2.75" cutout is 5.625 and min sealed volume is 0.18 cubes.