It's funny how you don't notice something, but once you see it, it becomes obvious.
On our new to us 2003 40 MDTS, there's a 20" x 14" panel hidden in the carpet between the bed and wardrobe. This panel has a tag to lift it out. When I remove the panel, I see it's only a couple inches thick and has heat shielding on the bottom of the panel.
It rests against a metal panel with four square head screws. My guess is that the metal panel is an access to something. Before I start taking things apart, I thought I would ask here - what is this mystery panel?