Hi Again Mel,
DO NOT WALK ON THE ROOF!!!! The roof is not designed to be walked on. You could put pieces of plywood up there over the rafters, but I think your better off on a ladder since a lot of water will be involved and it could become slipery. It is good to seal the roof with a rubber roof sealer after cleaning. Hopefully someone else will have a better idea on what to use on it, because I have never been successful with finding a product that will get out all the spots. Only my 2363 had the rubber roof (the 2653 was my parents, I never owned it, though I would like to find it to do so). On my 1550 and 2251, those came with aluminum roofs (which I prefer).
I must point out you need to thoroughly inspect the roof for any defect, tear, wear spot, etc, before putting any water up there. I realize your '99 is newer than my '94, but I made that mistake and still regret it. I ended up having a few small tears in the back corners, so with the scrubbing and large volume of water from the water hose, it went through the tears, soaking the insulation and making the inside ceiling panel deformed. Sure, I could have left it, but for resale value (I was concerned because I was preparing to sell it) I had to replace it, which could be difficult now since Sunline is closed.
Please, keep the questions coming! I love to help out someone new. After all, it refreshes my memory on it all, which is a good thing.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR