Ok, played with it a little more, did some sanding, it really is yellow under there!
Started on the seats, used some foam I had at work, some scrap plywood, and some plastic sheeting I use to Shrinkwrap boats, and some fabric I had for redoing the interior of my Baja Bug.
Does this look right? Or do the bottom corners need something done?
That fabric is what USMC uniforms are made of
Sprayed some waterproofer on it too.