We have just constructed a new 10 x 8 metal shed onto a new, very smooth concrete base which has a damp proof membrane incorporated into it. The metal base appeared to fit snugly against the concrete but after recent heavy rain the water has literally soaked right under the metal base and into the shed itself making the floor saturated. The instructions received with the shed (which was made in USA) does not give any suggestions for preventing this. I did think of applying clear mastic all around but before doing so, if anyone has any better ideas/suggestions, this would be much appreciated.