*9 warm side is ok 78 is on the low end of ok I personally would be concerned that the cool end temps (ambient air temp too??) would drop to far if the room temp cools much. Most racks are set up in controlled rooms 80ºF and 60% RH it is often considered part of the racks heating system.

I run a rack in lower room temps than you have, if it helps I can describe how I manage it.

The racks hot side is heated with 3 inch flexwatt This is controlled by 2 T-stat probes I found to keep the top correct the bottom was far to cool so I run a probe for the hot side top 2 and one for the bottom 3. The cool end temps are controlled by a strip of the low power 17 inch flexwatt controlled by a single probe of a third t-stat. It runs 79-81 bottom to top. The rack has 2 inch foam insulation on the top and sides the back is 1/4 with ventilation slots added. The rack is sitting on four inch foam to keep it from the cool room. The air flow runs back to front lower upper to lower, this allows the cool room air to be heated by the flexwatt. (each probe is also independently protected by a failsafe T-stat)

It was very complex to set up and perhaps un-necessary (just insulation might work) but I have accurate and precise control over hot cool and air temps that are inside each tub. The room temps from 64-80ºF do not change the tub temps more than a couple of degrees. Under 64 the cool end and ambient drop and over 80 there is no way to cool temps, so cool and ambient rise.