thats crap advice,
seal the hut best you can inside and get yourself a long piece of ducting as long as you can 4" minimum, old pipes anything you can get your hands on and seal and tape them all together, dig a trench from bushes etc in the shade, under a building etc, some where hidden to under your shed, it doesnt have to be deep, and run the trail of duct from the bushes somewhere in the shade, to under the shed with a 90 degree bend bringing it up and in to the shed and then cover and bury the duct, at the bushes end another 90 bend pointing up as low as possible to the ground, you will need to put a fine sponge aquarium filter over it to keep bugs out, and you will have to make a sort of cover that stops rain water getting in, a sort of chinese hat, or bucket upside down with small holes in sides then camouflage it, you will need to put an exhaust fan air out take on the roof or high on the side some where to let air out and keep rain water out too,. if your inlet fan is running constantly the temp inside the hut shouldnt be much higher than the outside temp in the shade, venting from under the shed will be ok for five minutes until that cool air runs out, because the air has to come from the surrounding atmosphere around the hot shed, not a dirty great big cool hole under the shed, if you use an inline duct fan they are air cooled motors and will run forever,. you can turn a little hard work in to a great little shed garden. if you want to use your 8" inline fan with a four inch inlet duct get a speed controller and turn the power down, a bathroom fan speed switch will do, a bit like a light dimmer switch, one will do from any decent diy store.
p.s.
our local supermarket has a gas/petrol station on the car park grounds, it has a long 4" blue and grey tube underground between fuel station and shop, they use a compressor and push money capsules through it to take the takings to the main shop, some work men were digging the carpark and broke the tube, scratching their heads as to what it was, so they knocked off for dinner, when they returned a money capsule was lying in the bottom of their dug hole, they opened it not knowing what it was there was £1200 in gbp $1947 usd, and did a runner with the cash, needless to say they were found out later that day.
