Cabover construction question 2001 Minnie 22R

[Wingnut23]

Help! I have a 2001 WF322R that I'm doing a total cabover rebild on. The problem is the sleeper board and everything past the metal bonding strip was complete mush and fell out when disassembled.
I get that on the strip, first row of screws go into the sleeper board, second into the lower strip. But what does the third row go into?
I have in the heap, a foot wide strip of bead board and two 3 inch strips of wood. Have no idea what order the bead board and wood goes. Hope someone has a little more information on how it was constructed past the metal bonding strip.

[Wingnut23]

Hear's what fell out. Can't find a row of screw holes in any of it.

[Wingnut23]

There's lots of threads on cabover rebuilds but are mostly old, unfinished and thier pictures are no longer working. My main concern is the 3/4 x 10" x 9' Styrofoam board that I believe was the next piece past the 1" thick sleeper board. The thing that bothers me is how Styrofoam could support any weight in the forward bunk area? Was it originally sandwiched between luan that rotted away? Any help or direction would be appreciated.