need tips on carpetting truck box

If you have the right carpet and you are not concerned with covering the back or the bottom then you don't need a pattern. The carpet can be stretched around the corners with no wrinkles. If I were doing this box, I would first round all the edges with a router or (if you don't have access to a router) sand all the edges.

With that box I would start on the front, stretching it very tight.

This is how this box was done, no seams and no cuts in the carpet