They probably need more ventilation in the top of that container. Use a thermometer on the floor of the brooder to know if they are too hot or cold. Yes they will poop on it, but it can be cleaned off. Many feed stores sell cheap ones for chicken brooders.
When did you get them from Rural King? How many days have they been with you? Day old chicks cannot survive without a heat source period. They have to be kept in 90-95 degree temperatures as soon as they are brought home in that box from the feed store.
People use heating plates just for chicks to keep them warm without a heat lamp, but here is a good homemade way to use a mama heating pad:
https://www.backyardchickens.com/articles/brooding-with-mama-heating-pad.67728/
Yes, check their bottoms for dried poops. Many chicks suffer from pasty butt, and if not removed right away, they can die. Warm soapy water water it getting the chick too wet or cold can get it off.
Here are some things to read and learn about raising chicks:
https://www.backyardchickens.com/articles/how-to-raise-baby-chicks-the-first-60-days-of-raising-baby-chickens.47691/
The Learning Center Under ”Articles” at the top of this page has a ton of info on everything from raising chicks to...
You can use a large cardboard box, bathtub, or large plastic Tote for a few days as a brooder. Many feed stores use the 50 gallon metal stock tanks, with a heat lumped clamped. I bought some play wood and built a brooder 4 feet long, 2 feet wide, and 2 feet tall. After a week, the top needs to...