Unless you are set on the cooler idea... two orders of these could probably do the trick
Sous Vide Water Cooking Balls by G&M Kitchen Essentials - 250 count with Drying Mesh Bag - Reduce splashing, steam, and evaporation https://www.amazon.com/dp/B01MUC26MW/ref=cm_sw_r_cp_api_sNNUBbPFMANRJ