just curious but how are you keeping the door from going in to the box when you step on it
I have welded two 1/2" wide strips along the longest sides of the frame just below the level of the door.

spray the outside of the box with the rubberized undercoating for reduced noise
I didn't get any road noise from the box. Just from the tools bouncing around inside when I hit a bump. That noise went away after installing the hatch. Of course I haven't yet taken the van onto a gravel road with the new box. I'm wondering what it will sound like then. Will find out next time I go camping.