Rebuild Cabover using Great Stuff?

After spending ten years of its life in the desert, our Minnie has succumbed to three years in Illinois, and has water damage in the cabover.

The luan on the drivers side was totally disintegrated, and I am now faced with rebuilding the drivers side wall.

For now, the filon is still attached to the roof and rest of the coach, and there’s a diagonal cross brace which makes it somewhat impractical to build a new sandwich wall. I also don’t want to mess with where the filon meets the roofline.

What I’m considering...

1) screwing external luan into the aluminum bracing, and gluing down the filon
2) building up a foam core using normal GreatStuff (1” gap)
3) attaching the interior luan to the bracing
4) filling the void with more GreatStuff

I’ve seen where some people have used closed cell foam for rebuilds. Yes, I know it’s messy, but at least I know it would adhere to the luan without question vs doubting if I have a solid sandwich wall, and it would also attach to the cross bracing.

Following that, I’ll replace the front filon with new product and eliminate the front facing window, which is where half of the damage originated, but that’s after I figure out the side wall.

Thoughts appreciated...