I don't have the knowledge to help, Peter, but I am surprised with the
amount of moisture ingress problems you have had. I have had my Oregon
remote temp sensor for a few years now and apart from a couple of battery
changes I have had no problems at all. On occasions I have left it out in
the rain and it even sat in some water in the bottom of my home made
Stevenson's screen for several days once. It's always been exposed to the
air, although covered from above, at least. Perhaps I have just been lucky!

Dave