Like jsmorphs said. I would put a thermometer on each side to watch. I love the pic but would do the bottom one a bit lower. If your worried about blowing out any insulation go to a local plumber and see if thy have any scraps of 4 inch schedule 40 or DWV pipe. They should give ya a peice if they have it. If not its cheap to find a small peice at home depot or lowes ect. Since you ar running 1 chunk of flex watt and treating it like 1 big space instead of 2 smaller ones you should be good with 1 thermostat.