I can’t help with a local dealer but can offer some thoughts to think about. I had some time to type, and your situation is sad, and a common theme nowadays. So maybe this can help others too.
Your 2007 T2363 is a great camper, and it sounds like you want to try and keep it. Pending your situation, that can be a wise choice or may become a great financial strain.
Now the reality, on some of the maybe to be expected costs.
It is common for a standard RV dealer to charge between $5,000 to $8,000 for a new re-roof and decking. This is not a guaranteed for-life roof, more like a total reset of what Sunline installed, but with new decking, and membrane, and they still use Dicor style caulking at all roof seams that have-to-have constant frequent maintenance. These costs are from pre-covid roof jobs. Right now, the large dealers are slammed with work, and many do not have the time or want to take on water damage repair. While some may do a re-roof for you, not sure if they will address the wall water damage and go after all of it or only what is easy to get. If you can find a smaller private RV repair place, the cost may be more favorable, just confirm how they warrant their work.
Standard large dealer shop rates can be $100/hr. to the latest, I just heard, $175/hr. While the rate is high, it is not so much the materials that will drive up the cost, it is the labor hours. Camper water damage repair takes many, many hours. It is the nature of the situation. This is where the cost goes very high, the labor charge.
If you have the ability to work with common wood tools, you really “want” to do this, you have a place where you are allowed to keep a camper for months (outdoors or indoors), this is something you may consider doing. Or if you have a family member who works cheap, this might be an option.
This also comes down to, do you want to invest in 1/4 and maybe up to 1/2 the cost of a new camper to replace your Sunline if you do a full restore? The whole Covid situation made the material costs almost double, and they have not changed since. That said, a quality restored Sunline of your vintage camper, is still better than many new equivalent-sized campers. If you like the camper you have now, it fits all your needs, and you really do not like what it is offered new right now, then restoring your camper can be money ahead of buying a new one. But doing restoration work is not for everyone. And then there is, how long do you still want to go camping? Lots of choices to think about.
Two years ago, I restored a 2005 T2363 for a good friend. The owners also helped as they could. The water damage was not seen from inside, but the moisture meter told a very different story. The restored camper is now better than the new as far as roof and siding sealing to keep leaks out. And the owners now have first-hand info on how to spot potential leak areas. Their camper will now last them as long as they want to use it, pending they stay top of looking for roof or siding seal damage and keep the camper under most any type of cover in the off-season.
It seems you found the moisture meter, and good for you. Sadly, the meter has never been shown to be wrong from what I have found. It can trick you sometimes, but once understood how false trips of high moisture can happen from metal in the wall, the rest is for sure moisture the meter is seeing. Before considering a full restoration or even a partial one, consider scanning the rest of the camper to see if there is any other water damage.
Buying any used camper also comes with risk, since you know now how to use the moisture meter, for sure scan any used camper you are looking at. Hidden water damage not even known by the seller is common. Your camper may be better off than the one you are looking at. Ans sadly, right now buying a new camper is not issue-free at all. I have had way too many friends buy new campers with way too many warranty claims and we are stuck trying to get things resolved.
I have lots of pictures of the 2005 T2363 along with others and I am glad to help show you what the restoration process may take if you want to consider doing the restoration yourself. Just ask and I get you some things to look over.
Here is an option to look at, this may actually be a little cheaper than a standard RV dealer with Covid pricing now in effect. They for sure will do the roof, not sure if they will for the chase the water damage in the rear wall or side walls, but you can ask. Or figure out how much of the damage you want to be repaired.
This organization does mobile RV roof repair, and they guarantee the work and labor for life, at least on the roof system. RV Roof Armor https://rv-armor.com/
They have a network of installers across the US. I am not associated with them; I just know of them and a good friend of mine had them a year ago to replace the roof on his 2004 Sunny Brook Titan travel trailer. His camper was a 30 ft’er with a full walk-on roof. They did a total tear-off, of the membrane to the decking. The decking was still all good and left in place as there was no water damage. They rebuilt the roof membrane in a series of primers, reinforcing cloth and top coatings on top of the existing decking. This type of roof uses no Dicor style caulking and is close to a maintenance-free roof, which is what they can guarantee for so long. You still need to look at the roof for trees and other outside influences creating damage, but the sealing of the roof system is what is guaranteed by the process they use. This cost was around $6,000 and took the one tech, 3 full long days to complete. My friend was fortunate he had no sidewall damage or roof water damage, just he had many failed roof coating learnings along the way and had to start over with a new roof. RV roof armor will do some level of water damage repair, you will have to check with them how much and if they will go beyond the roof and their rate for such work. Your camper is shorter but will need new decking and any water damage accessed. So, the cost above may be a little less in some areas and more in others. It may be worth a call to them to see what they can do.
Hope this helps,