No way I would put 200 lbs of body weight
on a Scamp
roof. No way - no how.
I do routinely lean a ladder on the side and lean over a little to reach things on the roof, but with very little of my weight
on the shell of the camper.
Can you put a step stool inside and stand on it to reach up (i.e. "escape") through the vent and do most of the work, then maybe reach the rest from the sides? If not, I would consider renting scaffolding.
Other ways have been used and posted before such as a temporary extension to an existing building, with the trailer parked next to it so the extension can be a work platform.