Even when you’ve controlled for factors that keep your system out of weather that postal employees would gladly march through you still have moist air and humidity. And in an enclosed system especially these become larger dangers.
Once you have trapped water you need to have a way to get rid of it, otherwise it will pool up and continue to gather until it’s a major problem. Even when you have a drain system you have to take other things into consideration, such as capillary action depending on the size and shape of your enclosure or separation of the water with other fluids that might be present in your system. Drain systems might also not account for very small amounts of trapped water that be dangerous nonetheless.
Porous materials could be extremely helpful if they’re soaking up excess water or extremely dangerous if other fluid leaks get into the system and bloat the structure. Many other fluids you might have present can be extremely damaging to different types of materials so you need an enclosure that’s strong enough to handle these other potential fluids while not unintentionally trapping rain or humidity.
Something that seems like a very small problem can become a very huge wet mess very fast! Interested in community feedback, any other seemingly small issues you’ve encountered that you’ve forgotten to design for?