For topical treatment to get the mites off the snake itself (provent-a-mite is not for topical use) the mineral oil on a cotton ball rubbed on the mites works but mineral oil causes scales to flake off too. Run to the pet store and pick up a spray bottle of topical mite treatment which can be sprayed directly on the snake.
For long-term permanent treatment get the P.A.M. (provent-a-mite).
Treat enclosure as per directions. Spray a thin line around the table or floor where the enclosure sits.
Vacuum and sweep your entire house and furniture very well to be sure there aren't any lurking.
Once you are rid of them, a partial enclosure/area treatment with the P.A.M. Every 4-6 weeks or so will ensure you never get them again.