I use Bounty Select-a-Size paper towels for my tubs. They usually work out to be 2 layers thick over most of the tub. For my 41 qt tubs, 5 half-sheets are the right length, but too narrow. I take two strips of five and lay them so they curl up slightly at the sides, and the middle of the tub ends up 2 layers thick.
EDIT: You can mist very lightly to raise humidity a bit, but not so much that the paper towel is wet. I'd say just move the water bowl over the heat to increase humidity, or consider running a humidifier in the room.