Siding corroding from inside out??

Why don't you contact S&S truck campers in MT. as they manufactured your camper.
406-755-5080

TG

electrolysis

For a semi-temporary fix, you may look into Eternabond tape. Search the forums for more info.

Your problem sounds like contact corrosion. Either something chemical in your repair reacts directly with the aluminum, or there is some water leak involved, or there is some metal (steel?) in direct contact with the siding behind the problematic area, or any combination of these. You need to find the root cause. A layer of plastic, or some tape or self-.adhesive plastic foil on the back of the siding may stop the process. But without knowing the root cause, you can not be sure.

I had one small spot on our previous aluminum clad TT that did this. As far as I cold tell there was nothing behind it.
I've always wondered what happened.

Thats unfortunate- fixing something twice is never fun.
Aluminum in direct contact or thru moisture with PT wood results in al corroding. Replacing the siding with more aluminum would require some serious isolation. Or replacing PT with non preservative wood, means undoing previous work. Using a different siding materiel that wasnt subject to corrosion might be an option since it needs to be removed?
aluminum+and+pressure+treated+wood
As to temporary fix, Eternabond tape likely would work. Assuming panel still primarily attached, though the tape is pretty strong. Some RV shops sell by the foot, or smaller than 50' rolls (5'10'20') offered by different sellers, Amazon Ebay etc. Not knowing extent not sure that metal patch needed. The tape should seal and keep from siding from blowing off- Temporarily.
Wish I could say I've never had to fix a fix that I had done.

The chemicals used now in pressure treated wood will eat away anything metal. All over US, decks and construction that used PT wood had the nails and screws corrode away allowing these decks to fall to the ground. If using PT wood, new fasteners on the market are designed now to eliminate this issue. Check the label on fasteners to verify. Your issue may be controlled by a membrane between metal siding and the PT wood. 30lb roof felt works great. Good luck.

The corrosive glue used for aluminium siding was big problem on RV back in 1980's
I would assume they figure out the problem by now, but sounds like they did not.
It is a cancer and there is only one 100 percent fix.

I repaired the seam under my cabover that had some corrosion with Eternabond. I just ran away it
All the way across worked well

thanks for the S&S phone number Troutguy thanks all that have responded so far.

The more I read the more I think it is corrosion, and it is because of the way I repaired it. Looks like I need to pull the siding in the affected area and add the separation. The original construction had about a 3/16" thick what I think of as "foam core" foam sandwiched between a paper like backer. Looked like a good additional insulation and stop and wind intrusion, which seemed like a good idea. Now it looks like it was for a different reason! The insulation fit with all the great craftsmanship I saw when I pealed back the skin. however, we did not have that material or anything like that and when reinstalling installing siding (with a time deadline of course for our annual family camping trip) so we just add some 3/16 plywood under-layment material to make up the thickness and add a little strength. In the suspicious areas treated everything with a rot prevent wood treatment stain like preservative. I don't remember the name will have to find the can, but similar to what we use to call it "wood life" growing up, except green, just like the green presser treated wood!

Fast forward a year, I bet the aluminum reacted to that "preservative" with just the slightest condensation, since we had an extra wet winter and I had to move to a pretty leaky barn for storage. With hint of moisture to accelerate the places there different metals touching - like staples, steel screws, reinforcement plates etc. So all extras I was doing under time pressure, without knowledge of the industry, made it worse, not better! I'll have to pull the siding, but bet that is what I find.

So once again, we are right on top of my family camping trip again! Will have to work out a tape fix, then pull the siding as soon as we get back and figure out what is going on. This time I am going to find some with aluminium sided RV repair EXPERIENCE to at least consult with. With all the constructions we have had in our area, should be able to find someone. I learned after we buttoned everything up the guy I had helping me, had only worked on fiberglass coaches in the past! ?Good wood worker, and mechanic... but no experience with this issue, and I sure didn't help matter!

Sorry to be so long winded, just frustrated.

Just one quick remark: If you do decide to use Eternabond on the outside, be aware that you will not be able to remove it again without damage. That's what the "Eterna..." apparently stands for ;-)