Re: wwyd buying from friends?
We had a pop up for my entire childhood, and it never molded or mildewed. The key is that if it rains while you are camping, you need to set it up once home to fully dry. I am almost positive my dad also used a mild bleach solution to rinse it after it rained on a camping trip (once home--bleach, rinse, fully dry).
I loved camping in it, and we often had our family (4 of us), plus two friends. It was nice that it felt like camping with the canvas walls that were more tent-like, but not like sleeping on the ground in a tent. We did miss the bathroom, but most campgrounds have nice washrooms.
Many things to many people.