Heat tape is just not getting that warm.

[bondo]

Adjust thermostat until temp under substrate is where you want it to be. Naturally you're going to have to set the thermostat higher to achieve the proper temperature in the tubs. But I don't think 3" tape in a 71 degree room is going to cut it. IMO that's too cool for a rack system.

I keep my room temp in the low 70s and have no problem with heat tape not getting warm enough.