I don't access my roof that much, so standing on the spare and climbing up works for me.
If I ever do decide to mount stuff on the roof, I really don't like the look or addition of a ladder. What I have thought of doing (if I need it) is to dig into the inside of the van in location X related to the outside so that I can add interior plate/strip as support for these:
Even just one or two of these mounted along the rear driver's side corner over the spare tire would be as good for me as a ladder. But yes, it would need a counter metal plate inside the van or the bolts would pull through your van sheet metal.