Stefan, I have Temp-est fitted to both of my Edge HD scopes, very easy to fit and worth every cent...however, make sure you have the side vents on your OTA as they replace those.
Failing that, if your OTA has the FASTAR secondary, TEMP-est also do a fan to fit in where that goes, so you'd be able to vent a lot of the hot air from there too. A Lymax cat cooler is an alternative there too, so long as you don't have an Edge HD scope with the correcting lenses in the baffle.
I find with my C8HD the side fans are sufficient as the temperature doesn't seem to swing that wildly in Sydney. Just be aware of the humidity, as if it's a humid night you will want to stop the fans once cooled to prevent drawing moisture into the tube. Once, I had dew form on the inside of the corrector, but not the outside
