Welcome! It sounds like you have a project ahead of you. And we have has many members in your same situation. We can help with the how to and what to do, but it will really help if you can post pictures of what you are up against so we can see to help better.
We have many members who have done rebuilds and restorations and are willing to share. Below is just a sampling of come more current ones.
To start with, your roof, you are correct, there is no plywood up there unless you had a special order camper with a walk on roof. Normally on a roof repair or water damaged walls, it is best to start with taking the roof and siding off and working from the outside in rather then from the inside out. At this point, you are past the how to start but we can try and help you pick up from where you are at and move forward.
Show and tell us what you have done so far as a place to start?
Here are a few rebuilds including total roof and wall correction. Some are completed campers, others are still ongoing. This will help show you what will sooner or later will come on your camper when you go to start fixing it. The 79 and 80s' campers below have metal roofs, but they help on the how the campers are built. The 2004 through 2007 campers below have the rubber roof like yours. All these posts help add something to a camper restoration as we all do them a little different.
A 79 Sunline restoration in process by Sunline Fan https://www.sunlineclub.com/forums/f...-mc-18647.html
A 87 camper restoration by YellowJacket https://www.sunlineclub.com/forums/f...ion-19403.html
Another 87 camper restoration by Thomascine https://www.sunlineclub.com/forums/f...air-17458.html
A 2006 T264SR complete post on rubber roof replacement, back and front wall repair on BenB's camper. https://www.sunlineclub.com/forums/f...avy-16834.html
A 2004 T2475 that is a work in progress. This has the front wall repair in a step by step description. This is one of my project campers. In time this will be completed. https://www.sunlineclub.com/forums/f...2-a-18706.html
A 2004 T1950 that is a work in progress until the Covid 19 situation stopped work this spring. This is a total camper restoration and one of my project campers. It shows how the camper comes apart and is in the process of being rebuilt. Lots of pic https://www.sunlineclub.com/forums/f...avy-17684.html
Here are 2 other project campers of mine in the take it apart and let it dry out stage. Again more to help show how they are built and come apart.
That may scare you big time... but these campers are all fixable. It will take time, but it is doable if you have common wood tools and the want to fix it. Feel free to ask away with questions.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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