Double boiler set-up. I use a stainless steel bowl atop a pot on the stove.....after the potatoes are made in the stainless steel bowl, i just place it atop the pot....you can cover with whatever fits.., foil or plastic wrap.
+1 with the double boiler. Also I've put the pot the potatoes are in into a larger pot of barely simmering water on the back of the stove or into the oven set at 200 F. Space becomes the issue though. Best of the season everyone!!!!!