ORIGINAL: cascadedad
I live in a pretty dry area with low humidity. After reading all this, I think I will just decap at the end of the day and then recap in the morning. If there is a rainy day, or something happens to warrent it, I will then just pull the nipple out and push the load out.

Also, I will be using a 3/16" thick wad card on top of the powder. The diameter is oversized and fits nice and tight down the barrel. This should create a very good barrier against moisture.