For previous posts search this Forum for `awning' then search the results for `mold'.
Here is my explanation. The awning folds are not air tight so during the day the air in the folds heats up and expands. At night when it is cooler the air in the folds contracts and brings the moist air with it. The next day the cycle repeats BUT not all of the sucked in moisture is expelled unless the awning is open. If that explanation is true there is no hope for a dry rolled up awning. Those awnings that have a solid cover over them when rolled up would not have as much temperature increase (not as much air expansion) so they should not suck in as much moisture as those that are exposed.