There are a number of moisture control devices on the market but most require access to the inside of the pipe bag, which means the bag would have to have a zipper.
For people that do not have a zippered pipe bag, our split stock allows you to use a tube style water trap without needing access to the inside of the bag. The stock is tied in as yu normally would but you are able to remove the top 1/2 of the stock (with the tube attached) to allow for cleaning, etc.