Last fall we got a good sized area--80'X80'--of pasture fenced for pigs this spring. We'll get 3 weaner pigs in late April and raise them to butchering in October. We're thinking of a corrogted metal shelter inside the pen. Do we need to make a wood slat floor or would a lot of straw on the ground do? Does that sound sturdy enough? What dimensions? Do those shelters anchor well into the ground? We're in Wisconsin. Any sources? Thank you!