Leopard geckos do not have more care requirements than cresties. Cresties require height to climb, and higher humidity. Leopard geckos require floor space (width), and lower humidity. There's no pre-made diet for leopard geckos, you feed leopard geckos strictly live insects. Other than that, they aren't that much different.
One single gecko can live in a 18 quart bin yes, but if the gecko is going to be your pet, why not place the gecko in a 20 gal glass tank so you can enjoy viewing it? But to directly answer your question, yes proper husbandry can be met inside a 18 quart bin.