Best way to tell, is if you have a ladder installed at the factory. Most Sunlines built with a ladder, have at least limited walk-on ability. If your coach was built without a ladder, there's a 99.9% chance that you do not have a walk-on roof.
To keep weight down, Sunline used a pressed fiber-type board. It is similar to Masonite, but not as strong. To safely get on the roof, you will need to get some canvas, or maybe even some blankets. Lay them on the roof and put some plywood on top of them. Make sure the plywood crosses several roof trusses.
Here is a picture from JohnB
and shows how he used canvas and plywood to clean his rooftop A/C..
If your coach does have a ladder, be careful when you get on the roof. Sunline would usually only produce a full walk-on roof as an option and only if requested. The Sunline fifth wheels (We've had two) had a 4'x4' piece of OSB at the top of the ladder and 4' wide OSB the length of the center of the coach.