bed floor question

[hotrodsbyray]

I know some of you probably have steel bed floors rather than wood. I bought a set of pine wood pieces for my 57 short step side, sanded, and then brushed on a blue 2-part epoxy paint from POR. [pictures to follow]. BUT now, like with so many of my projects i have changed my mind. I was gonna buy a newer (used) second truck for a work truck but decided to use my 57 and save the money another truck would cost. So I want to use a steel bed floor.
I am so long winded! Sorry. How do you attach a steel bed floor and not have the bottom edges of the rear fender and the step drop below the rocker and front fender lines due to the 3/4 inch thick wood not being there? Use spacers?
What gauge steel do you use for the floor and do you have to add extra braces under the floor to prevent sagging from loads over time?