I've only have 3 runner ducklings right now so I've kept them in a rubber maid container in the house to get them more socializing with people. Under the container I've put one of my seedling starting mats from the greenhouse. It's an ultra durable water proof heat mat designed to be on for weeks at a time to get seeds to sprout. No matter how wet they get their bedding it stays warm so they have very little risk of chilling. I do have a small heat lamp pointed down into one corner but they avoid it more than use it, even when wet. I will definitely be using these for all my little fuzzies in the future. The mat is about 1' x 2' and was about $25. I've also used the reptile heat mats from the pet store, but they are not nearly as water resistant or durable.