We've just had a red mite attack in a creosoted coop Clansman. They were mainly in the bedding but were crossing the treated wood to get to the hens (treated 10 months ago). The mite were in the panel joints as well, when I disassembled it. Previously creosoting on the inside and they have moved outside via the tongue and groove joints, which is why I now turn the joints upside down. If they do move outside they are then available to move to new premises. So I guess if you have never had them, fine. But when you have them you need to kill them all.
Back to original post about a fumer. I started my attack by spraying the entire coop inside with Nettex Total Mite Kill. I then left it closed up and in the sun for a few ours which fumigated it, to the extent that I didn't get bitten when I took the coop apart and didn't see any alive. Some may have escaped but I didn't see any.