I use this for heat for ducklings. It is a Victor Ultimate Flea Trap. The heat source is just a night light bulb but it is held in under the dome design to make a warm bed for the babies. Ducklings do not need as much heat as chicks so it is important not to overheat their brooder, which can cause death.
I also use washable shelf liner without any absorbant bedding as long as the tub has a channel for spilled water and the ducklings are higher than the water line. The tubs I use are about the same size as yours and I have plastic mats that fit in them so spills and poop go through the shelf liner while the ducklings stay clean and dry.
I hatch and raise hundreds of ducklings a year so I have found out what works without wasting resources on throw away bedding. Having absorbant materials such as shavings can kill ducklings if they ingest them but it also stinks far worse when it gets wet. It seems that the people who complain the most about how messy ducks are give ducklings the means to create a mess.
I feed wet feed but some people feed dry feed and then the ducklings have to either put their feed in the water or put water in their feed in order to wet it themselves. I add water to Purina Flock Raiser crumbles so it is the consistency of thick oatmeal. The ducklings will still clean their bills in their water so I use that water to wet the next batch of feed and give them clean water. The ducklings will get wet feed on themselves when they eat but they clean themselves and I give them baths, more because they love to play in water than to bathe in it. They love showers too and that eliminates the risk of drowning before they produce their own preening oil.
As long as you embrace the concept that ducks love water and they love getting wet, you will enjoy their antics. For people who are used to raising chicks and want to raise ducklings the same way, ducks can seem "messy" but in reality they are far cleaner than chickens (that bathe in dirt instead of water).Edited by Duck Drover - 4/9/16 at 5:30pm