I have often thought of building an enclosure for my vacuum. But I am
worried about overheating the motor.

The enclosure in Fine Woodworking this month is pretty close to what I
have often thought of.

Has anyone built one in the past? Did your vacuum overheat from lack of
cool air?

The problem I see is that exhaust air which is warm will be used to cool
the motor... Then the motor will be hotter, and the exhaust air will be
hotter... leading to a cycle that just can't sustain long runs anymore.

But I could be wrong...