It helps to use a thermometer on the floor of the brooder, and have a warm area of around 90 degrees under the lamp and a cooler area to get to. Totes can get pretty warm, somyou might consider another type of brooder.
Bantams can be very delicate at first, at least mine were when they were altogether in the beginning. After 2 weeks they seemed fine. A lot depends too on if they had any shipping stress in transit to the feed store, or if they were able to get enough food and water, or suffered from pasty butt. When I bring home chicks or they come in the mail, they all get their beaks dipped into the water and feed. Having a drop or two of Poultry NutriDrench can help too. I check for pasty vents every day for the first week, and for 10 days if they have it.