Hi psfarmer,
The issue is not so much the warranty as whether the roof was built with the structural support for a ladder. You should call Heartland Customer Service at 877-262-8032 / 574-262-8030. Have your VIN # ready. They can tell you if a backing board was built into the roof so a ladder can be mounted.
I think you might do better carrying a telescoping ladder in the storage bay or in the truck bed.