Seriously. you dont have to do much to treat racks.
Spray into the tub with substrate for like, TWO seconds. Air it out. and youre good to go so long as things are not WET. i treated.... 20 someodd rack slots and tubs and a cage and still have plenty of Provent a Mite left for a few more applications.
I had some weird little wood mite things, they were just white, and never got bigger. Strange. But the PAM killed them and i havent seen one since.
When i change substrate, ill just Spray that too. Prevention is key!