air sealing bath fan in attic

Just put in a new bath fan going into my attic and i ran it thru the roof and put insulated 6 inch duct. I've built a small box 'around' the fan and air sealed the box and was about to place the top/lid on this box when it occurred to me that 'perhaps' it might not be best. The fan mfg says it's OK to place insulation over the fan as it produces low amounts of heat. BUTTTT, insulation over the fan would allow that "small" amount of heat to dissipate. If I seal in the box then will that trapped heat be a problem. What are the thoughts of you people "out there""

 

Most fans blow the exhausted air over the motor, so I doubt it will be any sort of issue.