While there are concerns of high humidity, and its effects on the painting, it's really not a major problem as long as you adhere to two things:
- Getting the painting to dry adequately before shipping
- Avoid storage of painting in enclosed environment before shipping
These points serve as reminder to discourage mold bacteria from growing on it, before we even ship it to the location.
However, if you're still worried about problems with humidity, you may consider talking them into sending the painting rolled up (and in vacuum pack), and your customers can have them stretched using wood that is suitable for their environment. Hope you find these tips helpful