Our Coleman comfort double was great until one half punctured. I spent ages finding a p*nct*r* (bed inflated vertically in bath, rubbed down with the shampoo lather etc) before we went camping recently, so fixed this and it stayed up too. First night camping it goes down. Fortunately I'd taken a spare single. I've had another go at finding the p*nct*r*, twice. Can't find a thing. It's not the first patch, nor the valve. Dump it? Any other tricks?