Does moisture affect electronics?
Two situations I encountered: -

Situation 1 - sensitive electronic measurement circuit cooled down to below 0degC - no problem but, on warming and reaching a temperature just above zero, spurious signals and noise occurs - water droplets formed on the surface of the PCB - solution - dry the PCB and apply a good layer of water resistant varnish/lacquer - it never happened again.

Situation 2 - a power supply module located low inside a "fully sealed" enclosure - it worked for about 2 years then went pop. Reason, each night the box got turned off and as it cooled down it "dragged" warm moist air into the enclosure. The moisture settled on the base of the inside of the enclosure. This happened 6 days a week for about two years and there was about 1cm of water slopping around when it was inspected.

These are real events and both needed different solutions. Situation 1 was a totally open enclosure that was going through a design stage to see how it performed against temeprature cycling with humidity. The second situation was entirely different but equally problematic for regions that suffer high humidity.

My best advise is leave a hole for any water to drain out and have PCBs mounted vertically for least chances of problems.

My other advice is don't put reasonably high powered electronics in a wooden box - it's a fire hazard.