What is the interior panel called opposite the cab corner?

[bwilder10h]

I'm starting to get discouraged about all the problem areas with my truck. I bought cab corners and had intended to replace them myself soon but was under the truck last night and noticed the cab supports and panel on the interior (right inside the cab corners) have holes in them and need replaced. The ugly part is one cab corner I think is ok but that interior panel has a big hole in it.

What is that panel called? I didn't see it in the LMC book.

Without the means to take the cab off to replace all this, I wish I didn't have more than the value in it already as I would sell it and try to find one with less rust. I'm at a point now where it's not in a sellable condition for what I need to get out of it but sinking more money into it is going to put me where I'll have to keep it forever...