I don't have the details (call Fleetwood and ask), but basically it is a rather thin luan plywood skin over wood or metal cross members, then covered with a membrane (almost surely EPDM rubber on a vintage Storm). It's not very rigid and you can probably apply a fair amount of leverage with the satellite arm.
The dish is probably just screwed into the luan plywood. Even though the wind speeds are high during travel, things on the roof rarely come loose unless you actually hit something (tree limbs or overhead wires!). The forces are almost entire sideways (shear), not lifting or pulling.