After trying all the decal removal suggestions for years such as the 3M wheel, heat gun, chemicals, etc I finally settled on a 60 grit pad on an oscillating hand sander to grind most of them off. Then I used acetone on a rag together with a razor blade scraper.
Of course this assumes you are doing a complete repaint job and not just the decal areas because you will be sanding outside the decals too.
I first rolled the roof like you but decided to spray the rest of it due to low humidity drying the paint faster than I could work with rolling and tipping here the past month. I used marine bright white paint on the roof.
I also sprayed where the roof rolls around to the sides plus the front and rear caps.
Cleaning old silicon caulk off the side seams took two days for each side. People always say once silicon is used nothing else will ever again stick there. I suspect they just don't get ALL traces of the old silicon off. Guess I'll know in a year or so.
