74 Trillium rotten wood in front bench

[FluxCapacitor]

I have a ‘74. I noticed some cracking around the main shell attachment bolts in the front bench and some spongy fiberglass (see pic 1). I started cutting and found that the plywood “beam” that runs across the trailer that the attachment bolts go through is wet and somewhat rotten. I kept cutting and found there is more rotten plywood going up the front wall. The piece going up the wall seems thinner and is a different piece than the main cross beam. Was that board curved around the front lower corner the way it appears?

My questions are, has anyone dealt with this before? What did you do with it? I definitely want to replace the cross beam and attachment bolts. What about the plywood on the front wall? What’s the purpose of that piece???

Pics are here:

https://imgur.com/a/2zm1b2j