I build PDRs with 5.2mm plywood - pretty thin stuff. To have a floor, I'll need to support it or I'll just bust through when I step in it.

The webbing runs fore and aft - I suppose it would be easier to run it side to side, but I didn't draw p the plans that way. I believe it is very important to have holes in the webbing = both to lighten it and also to allow any water to flow between the partitions. I'd run 1x1 stringers on both sides of the top of the webbing to spread out the support.

I'd also put a hatch in the floor on one side so if I ever did get water in there, I could open the hatch, stand on one side of the boat, and swamp the water out.