I've found the best and cleanest way to rear ducklings indoors is a cage with a wire floor, i raise it above the bottom tray about an inch or two, place newspaper or similar in the tray and clean it out regularly as they make a lot of mess, i usually have some paper under where the lamp and feeder is so they are not on mesh all the time, but not near the water. the lamp is usually at a decient hight initially sitting on top of the mesh cage, then u can raise it as they get older, they can go outside somewhere secure after a couple of weeks if the weather is good.
best of luck.
mandy