A quick search revealed no other threads on this subject, unless I am using the wrong terminology.
It appears that there has been a leak at some point in the water compartment. This has allowed the (plywood?) covering on the bottom of the undercarriage to deterioate and sag. It appears to be a 1 piece covering from the front to the back, with a limited number of bolts securing it, to what I am assuming is the cross frames. The worst area is where the water tank is. From the limited sight line it looks as if the tank is supported entirely by this floor.
My questions are; Has anyone else had this issue? If so did you fix or return it to a shop? What the heck is the covering? My coach is a 99 Gulfstream, Tourmaster 40' DP.