Replacing Wood Wall Around Street Side Window 2518

Hi All -

Newbie here - just purchased a 99 2518. Its been great so far as I learn the camper.

The wood in the wall on the street side window is pretty corroded. The previous owner left the window open in storage for a bit, and it has separated from the panel behind it (masonite?) The more I pull up the wall paper more I expose rotted wood. Its not terrible, but it will need replacing.

I'd rather replace it all without going through taking the top clamshell off. I think I can get away with patching it. What are your suggestions on this? Can I cover it with more masonite paneling? What is the purpose of the wood there anyway? I've seen what Happy Trails did, but I really really don't think I need to go that far. The masonite of the "sandwich" behind the rotted wood seems fine and solid to me - its just that wall papered section surrounding the window that needs work.

Tony