Well, to be honest, mine is on an elevated stone platform which supported an old rotten wooden shed before I got the Keter.Sorry, in no way was I doubting you, but I was really unimpressed with the one that I had to assemble. It was about 600mm wide, 300mm deep and less than 1.8m tall. It had two doors. I didn't buy it so I can't remember the model number. I screwed it to the fence and had to lean it very, very slightly forward to reduce the amount of water that runs into it. That said, most of the water ran in through the "lid" of the unit- hence the need to seal each of the joins with clear CT1.
As for leakage through the roof, I have never seen a drop, and there was absolutely no need to seal any joints.
Perhaps they have changed the design.
I must say, though, that yours seems quite small: 12" x 24". I'm surprised that you can even get into it! Ours is about 6' wide and 6' deep, so I assume yours is a completely different model.

