Just watched your 4 videos. Its a cool looking camper. It has potential. This project would need a steady, methodical approach to complete. I would not touch the roof until the interior is completely gutted. Cover the roof with green tarps. That plastic you had in the video will not hold up for long. Anchor the tarps to the ground like a tent so you can get inside. Just keep any more water out while ripping out the interior.
Take out all of the appliances and fixtures and store them so that they can be reused or disposed of later. You might be able to shore the roof frame temporarily from the inside but the A/C units need to come down. At least from the inside you could safely assess the condition of the roof framing before proceeding
Way down the line new plastic covers are available for about $200 if those are cracked. White Fusion paint works too.
Good luck with your project. It might take a while but if you're up for it you'll have a decent unit and fun times.
