Careful with the mug warmer and thin bottom bowls.
Keith:
I too got me a mug warmer and a flat bottom, glass bowl. The bowl bottom just fits on the warmer plate and then opens up to fit a large brush, 34mm knot Vulfix.
One word of warning about the mug warmer: it can overheat the bottom of the bowl if you are not careful. So if you ever switch from stoneware or ceramic to glass or stainless steel watch out for overheating. Words of a scary experience. I nearly ruined my new $150 brush that way.
I solved the problem by opening up the mug warmer and adding a diode in series with the heating element. That cut the power output in two and is just right for the glass bowl. Just takes a bit longer to warm up but does not overheat the bottom. I usually soak the brush on the warmer while showering and that gives it plenty of time to warm up.