I built my own box, sounds great but looks terrible without carpet.
simple.just get the carpet you like.buy some contact cement at local hardware.apply cement to both carpet and box.you can use a small paint brush,but buy cheap ones you can only use it once.allow to dry to a tacky finish.stick carpet and trim.be carful once its stuck its there to stay.also have you thought about having bedliner sprayed on or do it yourself spray liner.check atoumotive supplier or local bedliner co.
I would walk into a local carpet shop and purchase a few feet of carpet. Carefully measure out the holes and whatnot of the box. After you have everything cut out use staples (your choice, just using an example) to get the carpet on the box. For best results try getting a thin carpet.
