I use Protect All cleaner and treatment, as Alpha Systems recommends. Seems to work fine, with no problems. As for the tarp, I would agree that you would get a lot of rubbing if there was a lot of wind. Same principle as a buddy of mine found out after he strapped a felt-lined tarp over his newly painted 1931 Ford Model A and hauled it down the road on a trailer. When he got to where he was going, the tarp had buffed all the paint off the outside of all 4 fenders. Learned his lesson the hard way. The rubbing on your roof would probably remove the exterior finish wherever it rubbed. JMHO.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.