I believe that Jayco will tell you that if a ladder was not factory installed, you should not add one, OR walk directly on the roof either. They add reinforcements under the roof so that all your weight in two places (your feet) will not bow the roof. Without the reinforcements that come with a factory ladder, you must spread your weight, either by putting down plywood to walk on, or resort to crawling so that your weight is spread out.
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.