Big big problem is that the cardboard is not waterproof.
Rain is one thing, one is usually aware rain is coming, or it is started so have to rush out to bring the stuff inside. But the real problem is that this thing catches the wind very well, and it was able to flip the thing despite of 5 kilos of water holding it down as a weight! And then the water flowing from the barrel soaked the cardboard, and it came apart.
Goddamn.

I think some glue and one more layer of cardboard will fix it.
Had to dry it out well, because the cardboard inside was still wet when the outside was already dry.
And somehow this needs to be waterproofed.