I don't know the size of your accommodation but in my experience, if their space is relatively small, they'll toilet all over it. If it's bigger, they'll pick specific areas as toilet sites and other spaces as somewhere to lounge around. For example, my trio have 4 trays in their shed but never pee in one of them. It's become a sleeping area, even though it's lined with megazorb and hay, exactly the same as the others.