I just flatten the flex against the bottom of the tank, tub, whatever, and tape the two 11" wide ends. Actually, tape the one 11' wide end, then tape between the wires at the other end. That foil tape is incredibly sticky, so make sure you've got the flex positioned where you want it before you tape it down. There's no pealing that stuff off! You can tape all four side if you want, but it isn't necessary. Jut the two ends will hold it sufficiently.