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With a focal length like that collimation will be an ongoing quest - perfection is needed and a combination of sight tube/cheshire and good laser collimater will be needed. Good luck with that!!
As for the temperature dropping just make a ply disk that fits over the back of your scope cut a hole in it that fits an 80mm computer fan and mount this, use foam weather strip (the stuff to go round doors) where the disk touches the scope to isolate vibrations and hold it on with velcro strips. This will help with initial cooling, will keep the mirror close to ambient as the temperature continues to drop throughout the night and will remove the boundary layer in front of your mirror. For better efficiency you can mount a baffle just in front of your mirror to force the air flow across the front of your mirror.
This will be a pretty touchy scope in regards to collimation and the effects of temperature.
Good luck.
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