I don't know if this is common knowledge or not but I recently discovered that putting the brush that I use to seal staves in the freezer keeps it from drying out. I've been using Cabot polyurethane. When I'm done sealing staves I wrap it tight in a plastic bag, put a clip on it to hold the bag, and then put it in the freezer. When I take it back out its still wet and not frozen. I've been using the same brush since late April.