SAFEST way to get on roof...OEM ladder or extension ladder?

Is the (fiberglass?) roof moulding sufficiently strong to take the localized force of the extension ladder? The curved transition area on my motorhome has a little sticker under the built-in ladder that says "Do not step here" and with good reason; it's little more than Filon bent to shape with little if any structure underneath. Obviously you have a different construction on your motorhome.