Some may have some spots that look like rot but they’re very localized. Never had mold I don’t think. Some cut ones had some white on them but that didn’t seem to become fuzzy. I don’t think I’ve ever seen potatoes sold in plastic though - unless you mean plastic nets, but I assume you mean like actual plastic bags or something. I empty mine on like a double layered cover of an old fan, so it sits in a big pan of grating basically. No active ventilation though.