I know we were talking last night about this lol, and I should have added some things.
Our room is cool all year round, we use flexwatt in the back for belly heat, and we have it running from the top of the rack and weaving shelf by shelf down to the bottom, so we only have to wire it once. The flexwatt being woven gives some more heat to the ambient temps, so you won't really have to contend with that problem. We have three sides of the rack insulated with that blue insulation board used for housing. One side is reflective (inside), and the other will be blue or black. Cut to size with a utility knife, and your good to go.
Our temps in the room consistently drop to 68 at night, so perhaps instead of pulling out the tubs the long way, have them go in sideways, just to minimize the distance from the heat tape. There will be enough room in the 32 quart for thermoregulating.
If you'd like, I can snap some pics of our setup, I hope everything makes a little more sense.