Remember, anything that's painted can benefit from the same wax/polish you use on the outside. Also, 95% of what you see on mine was done just by spraying degreaser on a rag and wiping up the dirt, then spraying tire foam on and wiping it off. If you've ever gone to look at a used car and was amazed at how clean the engine bay is...well they don't do too much more than that. They might spray it with degreaser and power wash it off but i guarantee you they use tire shine somewhere along the line (or something equivalent).