What can I use on the wire ramps of my cage so my rats don't get bumblefoot? The bottom is flat plastic and the levels have material over them so they're not hurting their feet. But I dont know what to put on the actual ramps from one level to the next. If I put something like coroplast, chances are that it's too slippery for them to climb up. But I am really scared for their little feeties thanks.