Soft sided six pack cooler from Walmart. $7 I bought a soft one with a removable hard plastic liner. Torch heat a nail to melt holes through liner (don't try to drill hard plastic, it will crack) , use an ice pick to punch a corresponding hole through shell and bolt it to the rack. Use big fender washers on the inside of cooler. Mine latest version has been on for almost 6 years. no problems. Liner will hold it's shape when empty.
. Cheap and dirty. When you are sic of it, toss it.