The only issues we might foresee are when our humidifiers are installed in fiberglass ductwork or also called "Ductboard,"would be maintaining the integrity. The integrity of the ductboard should be reinforced to accommodate mounting your Aprilaire model 600. Even though the model 600 only weighs 10lbs without water it could eventually create some sagging of the ductwork. If your installer has accomplished this then I do not see any other possible issues.
If you have any other questions regarding this or any other issues feel free to contact us.