when they are not roosting, you don't have to clean the underside, but when they do roost, they will poop on the top, so just rub a wet paper towel on the top to get the poop off every couple days
if you are using a cardboard box, wood box, or anything else like that, Do not, I repeat, do not use a heat lamp. I know they are cheaper, but instead, use a heat plate from Brinsea. It gives the chicks a chance to feel safe and escape the heat. They also work as a roost!