Appearances are deceiving - as well as names. This nice devices prime usage is not to cool my cat - rather to facilitate air circulation and exchange within C11 OTA to facilitate faster heat transfer and quicker accommodation of outdoor temperature. This homemade cat cooler was assembled from few pieces of typical drainage tubing (50mm and 32mm - 2" and 1,25" respectively), few pieces of wooden 8x8 mm dovel acting as spacer, a small block made from plywood and 40mm computer fan with protective grill as well as dust filter.

The fan when powered from 12V forces ambient air through the dust filter and inside the smaller diameter internal tube. At the end of the tube there is a plug installed which prevents the air from hitting secondary mirror and depositing there any particles which managed through the filter. A number of holes were drilled at this end with cumulative cross-section similar to the smaller tube. The fan also creates a small positive air pressure inside the OTA, which in turn forces the warmer air outside the OTA in the larger tube.

The airflow is not dramatic but overall the device seems pretty effective, in my experiments cutting the scope cool-down roughly by half.

Worth maybe half an evening of work and maybe $10, actually I had all elements laying around in my workshop.