Deja Vu ! I just built one....except mine is 7 shelves, but we'll call it the same I wired mine in series using 9" per shelf. My thought was that 9" is about 30% of the actual inside length of a 41Q Sterilite tub. I used the new Heat Tape from Reptile Basics because you can cut it @ any length (between heat elements). My only beef was that the heat is not exactly the same @ each position, but they were close enough. Mine has been in action for 10 days and my snakes are loving it

Best wishes and as always...remember your thermostat and plan on the open spacing for your wires. GOOD luck.