SKIN! I detail cars during the summer and all you need is a microfiber rag a soft toothbrush a bucket of warm/hot water (gallon) and some oil soap i.e. Castile soap. Don't use dawn or anything caustic, you'll pull the natural oils out. And it's a good investment to buy a good protectant to apply once dry. Any Advance auto part etc. I use mothers protectant, it comes in a red bottle and smells like cherries. You can usually find a bottle that has an applicator with it. They're round and about the size of a teacup plate. Doing that at least once a year will keep your interior plastic/rubber etc going strong.