The cooler I used was a small-ish (24-can) Igloo that I found at Walmart (on sale, too). Generally, you want to go for as flat a top surface as possible, but sometimes it’s unavoidable, depending on what else you want for the cooler. Mine had a raised, rigid tiling on top, but it wasn’t hard to fix. I just filled it with spackling and sanded it smooth. Super easy.