I'm planning to cover the feet with red clay dirt after a few months of setting, just to make sure it doesn't move. But, I can tell you that the frame is so stiff, that from side to side it will lift a leg before it twist.
The only way it seems to have any give is from end to end, it did have some sag in the middle before I leveled it.
As far as frost and freezing is concerned, in Ga. where we are, we have a 6" rule here. Most winters we only get a heavy frost. Only about every 10 years will we get a hard freeze. Same for snow.