I understand your concern, but...a bike is a piece of outdoor equipment. It's going to get wet, dirty, muddy, whatever. You probably wouldn't worry if you had it in a garage, yet the humidity and temperature in an un-air conditioned garage are the same as the air on the other side of the wall.
FWIW, my bikes have hung under my patio cover in the open air, protected from rain and snow but nothing else, for 30 years, in temps from -15 to 108 F. No problems anywhere.
I'm sure the Yardstash works, but it looks like a $100 solution to a problem you could solve with a $20 plastic tarp.