I should be a bit more specific. It still has to be solid enough to handle the weight, and level, but it does not have to be concrete or pavers, etc. So packed dirt, gravel, sand- whatever- is ok. I still would not put it on dirt, but there you have it. I wonder if it is more of a selling point in really cold places - concrete is prone to cracking in freezing weather, and if water gets in little hairlines and freezes, right? Gravel might be more reliable.
