Neil,
You have the option of resealing the roof every few months, or coating it once.  After tiring of streaks and leaks, and Mop & Glo, or similar, every 3 months, I chose coating with Rapid Roof III.  It is non slip, no streaks and can be re-coated or patched in the future if necessary.  I would recommend it for any coach. The outside of your coach was painted except the roof.  That is the problem.
Larry