If your planning on fattening weaners just through the summer, why not make a straw bale ark, cheap and easy and will last as long as the weaners, we did a temporary one with 6 bales, 2 high, 3 sides, and put a sheet of board on top, weighted with tyres! You can hold it all together with wire of some sort, I'm sure someone else will be along to advise!