if your planning on putting subs underneath your rear seat, there is no need for risers. i have an 01 supercab with 2 Kicker 10" under the rear seat. i didnt have to anything to the seat, and the seats still fold down and latch. However, i dont know if the 99's had a shallower floor in the rear, but i dont think they do, correct me if im wrong. the only thing you might have to do is buy some risers for the box, because it might be too shallow for the subs to fit.