SG19

I have an 06 8' box XL I bought mainly to haul stuff in and it has a rotten spot in the bed floor. I had considered getting a patch panel but it looks as though the cross member is also rotting. It appears that the cross members are welded to the bed floor vs the truck frame ? Body work isn't something I'm vary experienced with , thinking I could replace the bed floor and just Rhino coat the entire box.
Wondering if there's a bed floor replacement with cross members that can be welded in or is there a better solution to repair the bed floor ? I didn't pay alot for this truck and it's not worth doing an expensive repair with 250K on it.
Going to get a 4X8 3/4 sheet of marine grade plywood in the mean time to lay in the bed.

Appreciate any advise.