Thought I would post my mod if others want a cheap way to keep their phone chilled. Here are the steps and parts needed.
1. Drill a 50mm hole in the middle of cover.
2. Install 60mm x 60mm x 10mm fan and cover with zip ties. This keeps the weight down as much as possible and you won't see them as they get covered by the fan grill.
3. Attach the fan grill and solder a micro usb cable about 8 inches to the fan. You will have to cut both the fan wires and usb cable.
4. I used a velco strip to attach the small external battery to the back and you can't even feel it if positioned right. I also used one zip tie to the head strap closest to the dial.
Gdstime 6010 60x60x10mm 60mm 6cm 5v Brushless Dc Cooling Fanhttp://www.amazon.com/Gdstime-6010-60x60x10mm-Brushless-Cooling/dp/B00N1Y493Q?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00
Anker PowerCore+ mini 3350mAh Lipstick-Sized Portable Chargerhttp://www.amazon.com/Anker-PowerCore-Lipstick-Sized-Generation-High-Quality/dp/B005X1Y7I2/ref=pd_bxgy_147_img_2?ie=UTF8&refRID=1FVABJQ4X80JE3KF5072
MASSCOOL 60mm ABS Plastic Foam Cooling Fan Filterhttp://www.amazon.com/MASSCOOL-Plastic-Cooling-Filter-FFT-2P-60MM/dp/B00366YKO2?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00
I know its not the best guide but I tried. It came out clean and you won't even hear it run. It also keeps my S7 Edge not just cooler but chilled even after 2 hours of gaming.