I've got a four-tier one which I've had about six weeks.

Although I've treated it quite carefully in several places the seam has come away where the door is. It's poorly made and only has a single stitch through the plastic. Superglue has patched it up.

In fairly heavy winds its been ok, I've got a couple of bricks on the bottom shelf and a filled large watering can higher up.

I think it's best to tie the cover loosely to the frame so if it's windy air will pass through rather than push against it.