The pros fix it from the inside out and
never slit or cut into the outer skin.
They gut the inner wall clear to the outer
skin layer and install spacer rails so the
sidewall is smooth(er) like this (HHH) in the
framework underneath. They then use "The West
System" glue (same as for boat building) and
press on the outside exterior wall side with
hydraulic jack(s) to push in and flatten the
sidewall skin to the inner framework.
The cost is huge, same as having Winnie replace
the entire sidewall, and it is NOT a lasting
repair, no warranty. We were faced with it and
traded the rig off at a big lo$$...