I've never seen that before mate, it's a good idea. I got 3 pieces of tin sheeting and 4 8ft posts and 2 hurdles and put a temp pen up with some lorry sheeting on for the roof to put mine in for 24hours, ring them, put stockholme tar on them because I've got 2 active pig earths bordering the ground, then let them go. I may try some bags myself next year it would be easier.