I just built a rack with 4 tubs recently and used 41 qt tubs. I did belly heat with one continuous 11" flex watt that weaves back and forth up each shelf. I cut all the pieces on a cnc router to leave cutouts for the flexwatt to go from one shelf to the next. you could use a hand router or hand sander since flex watt is so thin. I have one cheap rheostat lamp control and a hydo farm thermostat just in case to make sure they don't get too hot. The rheostat control is cheap- 12$ so the thermostat is a safety back up I guess. Works great so far. I also painted the exposed edges and sealed hidden ones to help the mdf from warping. I'll try and get pics up soon. The ambient air holds around 80 and hotspot at 90. just a little input for ya