My custom platform. I did the rattle can truck bed liner. Came out pretty good. Less than $100. 2 layers of 3/4" dense plywood.
I used dimensions from the newer stock platform but I made mine 24" deep instead of 30. All angles were same as newer stock platforms. It looks like this is exactly what you did 2500HD...
http://tapatalk.imageshack.com/v2/14...212b85c784.jpg
http://tapatalk.imageshack.com/v2/14...20b0893b68.jpg
Surfin USA