Hook,
You don’t really need rollers or locks. We have built a couple and used a thin acrylic plastic for slides on the bottom of the drawers. As far as locks, as long as your tailgate locks and you have a topper that locks, I think it would be almost impossible to get into it. You just have to make sure you make it long as possible so it fits tight, front to back. That way, it would have to be lifted straight up to pull it out. We used 5/8″ or 3/4″ plywood for the top and bottom so even empty the thing weighs a bit. I used 1/4″ plywood for my drawer bottoms and my brother used 1/4″ masonite peg board. I think I have about $70 into mine. (shortbox F150) There are a lot of different things you can do. It comes down to what you want. If you have any ?’s, PM me.