Yep.. Our one is very similar.. not quite as bad though.
I pulled the fuel tank out and could see the sky. poked around with a screw driver and the true nature of the rust problem revealed itself..
Must have been the same person putting silicone everywhere.
Needs some new boot floor and the back 3 layers of spot welded seam needs to be pulled apart and some shiny new metal welded in
Will put up some before and after pics when done.