I put 3 1X3s down the length, after Dynamat & foil-backed insulation. I then used 1/8 Masonite in 3 pieces(crosswise) covered with a foam-backed headliner material. Contact adhesive held the Masonite to the 1X3s, GOOD spray adhesive held the headliner material to the Masonite, and screws held the 1X3s to the ribs. You'll have to be very careful to get the edges lined up along the sides(mine are exposed and the headliner wraps around) and make sure you cut carefully to match the side and front contours. After you get it all up, wrap some screen molding(cut to length, with tapered ends) and using a brad nailer, nail the cover strips over the joints into the 1X3s. I really like the way mine turned out-I even added a mini console to mine. I had found some seats from an 04 Nissan Quest that only needed cleaning for $200, and had sent the skirt from the front seat to a fabric company so they could match carpet, headliner, and some vinyl(which I haven't used on anything yet). I'll try to get some pictures to put up somewhere.
