In June, 2010, I managed to clean the RC mirror and chase an extremely distant galaxy cluster Abell 2151 in Hercules under very warm and humid conditions (75 degrees minimum/near 100% humidity). I did 11 hours of LRGB on the cluster with the RCOS and Apogee unfrosted at -20C.
http://www.robgendlerastropics.com/HerculesClustertext.html – Abell 2151 galaxy Cluster info