I used a grass mat behind our 75. It was one of those beach mats, I mostly used under cars, so I cut out the best part and taped the edges so it would'nt unravel. Not a great pic- I'm inexperienced- but grass mats look natural and if you don't want real dark. Also, try roofing paper. It has 2 tones and is moisture resistant, you can crinkle it or fold it for contour.