I gave up using the thymol. I found that the vapours tended to condense out on the object involved. I stored the Kiev which started this thread with a little sachet of thymol inside the body and after a few weeks, found liquid thymol on the shutter curtains. Logically it should evaporate off again eventually, but I'm still waiting! Also it appeared to have no discernible effect in slowing the spread of mildew on a camera case.
I have used the paraformaldehyde, heating the crystals occasionally to help the production of the formaldehyde gas. I found some data somewhere online (though I cannot locate it at present) which stated that formaldehyde fumigation is only really effective at ambient temperatures over 20°C and relative humidy over 75%. The latter isn't a problem here, but the former rather limits its use to a couple of weeks a year!