To start, that sucks.
Are you sure you have mites? They are small and black, they look like poppie seeds or pepper. You find them in the water bowl often. Hard to see on the substraight.
Mites are very unlikely to be found on the aspen unless it has been used before by a snake with mites. They won't stay in the aspen unless there is a snake there for them to feed on.
If you really have mites, that sucks.
I can't find a link, but look for a link using Nix head lice treatment on mites. You mix a full bottle (59 ml) of nix in a gallon of water and spray snake and area. I tried it on some Rough Green snakes a few months ago and it worked very well. It's been debated on this forum but I can't find it right now.
Sorry to hear about your mites, that sucks.