Hey guys,
I had been wanting to do this to my FG trey for years now and finally did it. However, I got a pro to do it.
PFA blueprints of the Fg trey.
The next photo is the work done to my tub. Thick marine ply was set down and bolted to the cross members, the anchor rails, and tool box screwed into the wood, and then marine carpet.
Ps. I know I'm replying to an old post, but this is more for the people who are looking to do something like what has been discussed.
Cheers