If you look at kicker's web site, The 15's only need 1.5 - 3 cubic feet each, so a box made from 3/4 mdf wouldn't be too big or hard to make, I had 2 comp dv12" in my old boat with 2 RF mono 500s puching them and it only rattle your insides, But put covers over them or you will get a ski push into them ( experance)