I have heard that carrying ladders, bicycles. etc. on a ladder can cause enough movement that the sealant on the roof where the ladder attaches can be disturbed enough that it can cause a leak through the attachment points. No first hand experience, but a friend I trust.
Elliott & Vicky, and Sadie the GSD copilot
2014 36RE, Onan, Titan disc brakes, 17.5 inch Sailun H tires, lots of other options
2013 RAM 3500 CC, LB, DRW, Cummins, AISIN, 4x4