I havn't managed to dent mine yet, only Luck so far ,but you got me to thinking....
If I knew definitely that the Rib was compromised ie pushed in somewhat, and was very noticeable, well I'd consider drilling out the Rivits along the dent to relive further stresses on the sheets and with access from inside put long set screws ie long thin bolts through, a wood chocked Steel Beam with same hole spacing's then nuts on inside, then with a spanner start n tighten.
Hopefully someone or anyone could tell If this folly or not? Done slowly with a good shock every so often from a ball pein to help set itself .
Duno just Duno???