I've heard everyone recommend taking these step units out for the winter season..I just wanna know why..will they crack if the top layer of water freezes or what..our winters are usually kinda mild..maybe a week of snow & temps in the 25-35 range, usually more rain than anything. we just put the steps in a 27 ft ag this summer so wanna know what to do next. They were a pain to put in (screwing in the pebble filled ballasts) & don't relish the thought of taking them out & in & out & in