I have issues with the secondary dewing up on my 300mm reflector. I know that dew heaters are the preferred method but I like to minimize power in the field so I considered another option. A flat disk whose circumference is the same as the footprint of the secondary mirror. Mount this disk above the spider in order to shield the secondary from super cooling due to radiating into space. This may be less than ideal when working at 45 degrees but I mostly observe at or near the zenith.
Will this work?
If so, what would be the best material to construct it from?
Any thoughts, opposition or support, are appreciated.