A travel trailer won't ever develop mildew issues if it is maintained dry. However, since the majority of RVs are kept in storage for extended periods, problems can develop that lead to mildew. Always wetness combined with a lack of ventilation is the cause of mildew. For more information on how to prevent mold in RV during storage? Then read our blog post.
https://www.storeboard.com/blogs/business/how-to-prevent-mold-in-rv-during-storage/5560833