I've found that in our wet climate in the UK the majority of caches are very wet when I open them. Most caches seem to be plastic boxes with a tightly fitting lid. You would think that this would keep the damp out but it doesn't seem to. I remember seeing a theory somewhere that this type of container actually makes things worse because pressure differentials between inside and outside can cause water to the drawn into the container - and once inside it can't get out. The driest cache I found was actually an old metal box with an overlapping lid, but not sealed in any way. I would like to start creating a few new caches of my own soon and I would appreciate any advice on this?