The maintenance manual cover most of the access and a small mirror or view scope make inspecting the lower half easier.
If it really is solid then count your blessings and make sure the drain/weep slots on the bottom are open.
Personally I hosed them out with a pressure washer.
Ospho (Phosphoric Acid) as a way to deal with the rust.
Reapplied then washed the Ospho out
Dry completely
Rolled 2 coats epoxy primer
Shot the seams with Eastwood Anti Rust (A waxy self healing sealer not a rust converter)
it's easy with the windows removed and if you're not Popeye
