I used some thin green "felt" carpeting in the engine room of my Burger on top of the steel (white painted) diamond plate. It was fantastic and lasted years.
Elevations - Color Leaf Green Texture 6 ft. x Your Choice Length Carpet-7PD5N620072HO - The Home Depot
And before you start making comments about growing grass in the engine room, note that green epoxy floor paint is what we always painted the train repair depots in. I don't have any project photos handy, but the below gets the point across.
http://3.imimg.com/data3/KN/IO/MY-35...or-500x500.jpg