I have never had mites yet....however....Provent a mite aka PAM. Everyone I know that keeps snakes uses this and swears by it.
I am not sure what you are doing with the pest strips but do NOT put them in the cage and the snake will find a way to get stuck to it.
Also switch to paper towels as you can see them easily then. Get rid of all substrate. If you have anything wood in there....bake it at 250 for an hour.
When cleaning make sure you get it good around the top of the cage as that is where they lay their eggs. Also and this is an interesting point. They spread so fast as they do not need 2 to lay eggs. 1 mite can lay eggs all on there own. Egads.
Oh 1 more thing....hides and water dish should be put in the dishwasher on a hot extended wash.
Good luck!!