I have a 2008 f150 4 door 4x4 . i would like to build or buy an under the seat box for 1 shallow mount 12 inch MA sub .I do not want a plastic box they are 300 bucks and thats crazy.any help with this would be great . if a sub has 800 watt max and RMA of 400 what size amp would be best all are running at 2 ohm amp and subs.