Dimensions of the trunk? *Might* be 5cf in there, but 8 would be pushing it. might want to try a pair of 12's, or even some 10's and give them enough room to breath. Most 12's can do sealed in about a foot or so, some 10's even smaller.
Guy on youtube has one FI Q 18 ported and its around 7 or 8 cubic feet, he had to fiberglass the wheelwell to get the additional airspace let me see if I can find the vid.