True, but unfortunately the slide seal/wiper doesn't always get all the moisture off. Sometimes the slide roof isn't perfectly flat and some water can get carried in.
I would have your RV dealer inspect the slider roof seal/wiper for effectiveness, at least for piece of mind that everything is fine.
I have a multi-purpose ladder I carry with me and inspect my slider roof before closing (remove twigs, acorns, etc.), and will drag an old beach towel across it if it has water on it before closing.
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)