Smoothing out the bed

My bed inside is rotten, dented, and just ass ugly. This winter i wanna put just all flat sheetmetal on the bottom, and sides, and back. What do i do with the stock boxrails that the box bolts to the frame with? Can i just use Stainless roudned top carriage bolts and bolt the flat sheetmteal to the frame? I plan to have the flat sheetmetal sprayed with bedliner. Any suggestions or tips on doing all of this. Thanks in advance.