Hi,
Make sure that you remove ant spare bits of wood that your OH may have used,, We had a big problem this year with a 6X4 tongue and grove shed, we wondered why they kept coming back so quickly, then we removed the spare bit of wood over their entrace, it was crawling with them.
This is the worse year I have known for red mites, I have been useing thick bleach with a splash of Jeyes fluid, watered down to use in a power sprayer, I used to just use thin bleach and that kept them under control.
Michelle xx