.2 cubic feet matter?
 

i making a box for my friends truck for 2 infinity refrence sereis 12 inch subs,i can only fit 3.8 cubic feet and the subs call for 4 total ported, will this make any diffrence ? line it with poly fill?

Minimal difference - remembr to lengthen the vent and it should be fine.

Personally I always like to line at least two walls inside any enclosure.