Opening an airtight case or camera housing can be tough when traveling from altitude to sea level. Try putting your case or housing in the refrigerator or freezer for a few minutes. Opens easy after that. 

Start saving the silica gel packets you get with various products. Before a trip, put them in the oven at 175 degrees for 15 minutes. Then put them in a ziploc bag to keep until you need them.  When you need to protect a product from the humidity, simply place the item in the bag and re-seal it. The packets will absorb the moisture from your precious electronics.