Hi Bert,
Thats the idea, but I would have the cold side of the Pletier only in the Bag with its fan to circulate the air and not to keep bringing in and cooling outside air, An insulated duct is required also ,Fan vibration wouldent matter if the lot is not conneced to the Scope/Mount, as regards a Fan ive seen some large CPU fans that are just made for the job they take the air from the centre and push it out the sides, or use a CPU Heat sink with large fins and blow the cold air through it with the fan, or lift it through and outwards by reversing the fan direction,by the way look at
www.oatleyelectronics.com they have Peltiers at a good price.
cheers....Jim