Just occurred to me could use torch to help remove some of the old goop. I mean very minimal torch use so I don't burn it down but the warmer it gets the easier it comes off. Sealing a porch roof, to the trailer is about impossible on a mobile home. On this old trailer the J-track that is screwed onto side of trailer is used as a really mini rain gutter. IMO, ultimately, the J-Track should come off and flashing should be run behind it, then over the porch roof. But still have to get roofing material sealed to trailer. I'm just not sure if the peel & stick roofing will adhere to the trailer roof. Ultimate way would be to do porch roof with EDPM run up on trailer 2-3 feet, then EDPM rest of trailer roof. Trailer EDPM would overlap porch. But again, roofs need to match with no big steps to tear/stretch the EDPM over time.
I'll finger this out!