Here's an update, it doesn't look like my strategy is working very well. After three days I had one tub with a major infestation again. And I have the small fire pied that didn't look so well, so I wiped him down with water and put a wet paper towel over him, checked on him after a few hours and he is looking much better, was just super lethargic.

My new strategy for the tubs is to move each snake to a freshly cleaned tub every day or two, will probably not wipe down the snakes unless I see a mite, then will just spot wipe them. I'm also spraying the tubs with mite spray, wiping them down and keeping them damp and letting them air dry, i.e. more prolonged contact with the mite spray. Then after about five minutes I spray them down with water and dry and put new paper towels. This time it seemed like most of the mites were under the paper towels. Perhaps it was the eggs left in the trays that hatched out?

My hope is that with more frequent cleaning of the tubs I'll remove all of the adult mites before they can lay eggs and break the cycle.