Talking about the weather is like a national pastime here in Ireland too .
I've never seen a dry spell like this in my lifetime ,what small amount of rain we have had in the last few months is gone within a hour or two of hitting the ground ,RH98% that does sound uncomfortable . I was never bothered too much by hot temps ,I did get a taste of the 'Sirocco' one time while on holidays in Morrocco,was upto about 47C in daytime and still remained high 30's at night ,on top of that I got badly food poisoned .So spent a few days very very unwell ,sweating tossing and turning , luckily glass litre jars of the freshest sweetest orange juice I ever tasted was easily available ,they did have nice confectionary and pastries too .
As far as I know Audio Note do use impregnated and laminated wood fibre boards in some of their very high end units ,its also very thick maybe 5-7 mm so it also provides great damping for any components attached . I guess a simple home made laminate board probably isnt going to resist in all climatic conditions ,but it does seem like it can be done ,I still cant seem to find any links to the Japanese guy who makes it though .The warm running nature of tube gear does of course help drive off any water molecules that might be present in the board material ,but this virtue will of course work against you as the board will absorb a certain amount of moisture when not in use .
Heres an interesting doc on wood moisture content ,
https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf
Looks like spruce is one of the best ,I think thats also commonly used here for electrical and telegraph poles here .
