There is one preventive measure I didn't see in your post regarding
Brownie's experience of being overheated.  You can use plastic soda
bottles filled with water, capped, frozen and wrapped lightly in a towel
to place in Brownie's cage to help cool him.  I have done this on
occassion with my ferrets when they are playing in their rabbit cage
outdoors on hot days and it has worked out well for them.  I keep the
cage in the shade and add the icy, towel wrapped soda bottles as a
cooling toy.  My furkids have even curled up next to the bottle and
fallen asleep.  Of course I watch them constantly for any signs of heat
stress and bring them back indoors if I notice any panting or other
signs of distress.  I also keep a plastic pan with an inch or so of
cool water available for the ferrets to splash in.  Sometimes I add
ice cubes to this.
 
Fans don't work with ferrets in the same way they do with humans, as
ferrets don't have the ability to sweat.  It is the action of the breeze
from the fan evaporating the moisture from the perspiration on our skin
that gives us humans the cooling affect we feel from a fan.
 
I hope this helps you.
 
Cordially,
Greta Hoisington
[Posted in FML issue 4176]