sew cording to the edges of the vinyl and make the cover a tiny bit smaller than the box(so you cant stretch it over tight). also use some spray on glue between the vinyl and the wood so it doesnt flap when the bass hits.......i covered my first box that i made with vinyl.... maybe i can get some pictures up.....
I dont know if you can see the seams.. My mom did it all for me. She sewed the seams and turned it all inside out and stapled the excess material after the seem onto the box. We unfolded it so it wasnt insideout as we put it on the box and kept stapeling the material and folding ofertop the staples. Its kinda hard to explain because i dont sew much. It all looks so straight and good. Like Archie Clark said, make it a little smaller than you need because it will stretch and look alot better than the saggy material if you dont make it smaller.
haha, i have no more money after buying mom something nice, lol. They usually have a large variety of vinyl at any fabric store.. but im not sure about diamond plate. Ive seen the interior of a car done in diamond plate vinyl and that looked really nice! Maybe check ebay.. thats where my sisters bf got the stuff he needed for a poker table he made and other things.
My box was done the easier/cheaper way were it was just wrapped in vinyl then on the sides that were left the vinyl was pulled and stapled in and I had other pieces of 1/4 inch wood cut to the size of the sides and covered also, then put on top. I know I wrote it like it could be really complicated but it really wasnt. I did blue vinyl and carbon fiber vinly which i think came out pretty bad a$s.
The side pieces where just screwed in on each corner and that did the job. On mine I used glue but I also stretched and stapled it so it would stay tight and not move around while the glue was still drying