I put foam pipe insulation on the edges and hold it on with plastic zip ties. This allows you to wedge it between the front and back of the tank so it stays in place pretty well (if it isn't wedged in place though, the foam makes it float). This is basically the stuff I use: http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053