Yes, Creosote, the real stuff. That in combo with the flame thrower and DE has been enough for us. We apply the DE to the hens as well (logic tells us that some mites must hitch a ride on the birds, or they wouldn't spread). Our first ever hen house, which was at least 3rd hand, maybe more, was so infested we set fire to it and started again, with a converted garden shed.
To avoid mites down your neck while you're cleaning the house, get a white paper suit from somewhere like B&Q. They are cheap, disposable, have a hood and sleeve cuffs which can be tightened (nothing's 100% against mites but it does help) and stick them on the bonfire afterwards. Then scrub yourself and any clothes you wore under the paper suit. Wear tight rubber gloves too, over the wrist cuffs, and wellies with the legs of the paper suit tied with string. It does look funny but who cares