I've had thumb issues too, and this summer I really started looking at ways to keep my thumb dry and also to stop clutching the ball. (No offense to Clutch here. He scares me, and I really want to stay under his radar.
)
In June I found a perfect thumb "cocktail" so to speak. First, Ron's Magic Carpet; add to that a thin strip of Hypafix medical tape to the back of the thumb; and then keep a pile of those nifty alcohol towelettes on hand for when your fingers and thumb get sweaty or oily.
My coach thought I was nuts at first, but the result has been pretty good, so he's a believer now. My average was up +13 in summer league since I started this little ritual.
Coach told me the other day that one of the "big" bowling companies is coming out with some alcohol wipes similar to what I've been using. I just buy the ones they sell in the drug store with the diabetic supplies, and coach and I agree that they're probably cheaper than any speciality item that will come from the bowling industry.
Anyway, try a few different combinations of things to find out what works for you.
Good luck!
Deb