Bleach and baking soda will fix that cooler smell.

Clean it with a dilute bleach solution after each use, then dry it with the lid open.

The smell is usually old mildew or bacteria that hid in a crack or a sealed-in damp spot. A good scrub with soap and water isn’t enough — you need something that kills the biology. A capful of bleach per gallon of water, wipe down every surface, let it sit ten minutes, then rinse thoroughly. That nukes the source of the smell.

After cleaning, dry it completely. Leave the lid propped open for a full day in the sun or near a fan. If you store it closed while still damp, you’re just starting the cycle over.

For maintenance between trips, toss in an open box of baking soda or a crumpled newspaper. It won