Box Truck install question

I have a couple of box trucks to finish up and I used scaffolding to be able to reach everything on the sides and back, but I can't for the life of me figure out how to get to the front of the box that's right behind and above the cab. I don't think that climbing on the cab itself would be a good idea, I think I'd cave it in.
Any thoughts?
Any help would be greatly appreciated!