What I posted above is the correct seal and the correct method of what we use with that panel. Don't tell anyone but I own and manage a mobile home park. I would remove the drip edge and loosen the mobile home roof where the room is, insert my flashing under the roof, refasten the roof and then use butyl tape to seal the gutter. You would want it to run down to you R panel and then a sharp corner so it would almost be a L shape. As flat as that roof is I would think the flashing would come out on to your R panel roof at least a foot. I would install two separate rows of outside seals like I posted above.
Below is a picture of a roll of butyl tape. It is the same thing your drip edge and your windows were originally installed with. They also sometimes use it between the seams of the R panels if they are worried about water penetration happening. I buy it by the case.
