In the words of a very wise friend.... I have 3 words words for you, duct and tape!Thanks Them! Say hi to Rider for us and stay clear of his needles .
Covering the door from the outside is the easiest but I doubt my wife will go for that. So I have to figure a way to be able to seal it and close the door behind me. When I had a darkroom in my kitchen in NY I used blackout shades and a boatload of velcro!
So I am growing in the bathroom as you may or may not know? Lol. Well I enclosed the tub space for the same reason. So maybe build a dark space within the shed using like 95% of the available space. Which is to say a few inches in from the door opening put up overlapping panda paper. So you have the shed door. Then the panda.
Also if I may suggest 2 cheap duct booster fans for exhaust. You know what works great for a light proof vent?!?! Lmao. So you grab some 90° aluminum......
That's a joke. But if you can keep it dark and lots of air moving, you're gonna have a heck of a bloom season son!!!!