Sometimes in life you get a do over.
 

Discovered we had some soft spots walls in our HiLo. Disapointing since we did major water damage repair in 2011/2012. Upon further inspection discovered a few spots of caulk had failed around the dinette window. Found a slit in the fiberglass in another spot. Our 1990 25ft. HiLo is suffering from 28yrs. of slamming down highways. DH and I our not real good at fiberglass repairs/painting exterior. Advice when your eye sight isn't that good use a magnifying glass to inspect caulk around windows. DH plans on scraping caulk from all windows and reapplying in the spring summer. Went out camping and we had some serious rain. All the interior repairs held up. Was a chalenge to undo the HD liquid nails from previous repairs. Got lucky as we had underlay and paneling from previous repairs. Had to buy more seam tape,foam insulation ,caulk and HD liquid nails. Advice..just because you recaulked all windows a few years ago carefully inspect every year. Now as posted before about our ref. not lighting..DH used the stove for some heat while doing repairs. His conclusion was that he had more gas in the lines and that is why the ref. lit up with no problems. Now to fix the leak under the kitchen sink. Then winterizing and putting the cover on for the winter storage. New name for the HiLo Patchy!!

I have the exact same issue. Really rainy summer in the East. But now I'm here in "dry dock" in Arizona. I can actually see into the exterior walls from the outside (in a small place.) Obviously, some dry rot in there. And I haven't the first clue as to what to do to make things better.

How do you do something, other than ripping the exterior walls off? Which I cannot imagine doing? Any way to seal things up? Advice would be appreciated!

Repairs
 

I would think that you would use fiberglass cloth and 3M Bondo to do repairs. This would be on the exterior. If you were ripping out walls from the interior then rip all the way back to the fiberglass. Bondo the interior wall/fiberglass. Build back your layers the same way they came off I used some Externabond tape on the interior slit before we put the wall back together. Use HD liquid nails to bond all layers. No it doesn't eat foam insulation. These instructions are for a fiberglass classic model. With a Towlite you might have to work from the outside in. Use plenty of interior bracing. E#xternabond tape comes in white and almond.