Only way you’ll know for sure if the underside is solid is put it on a lift. Couple things I noticed: underside of the hood is rusty; not terrible, but indicative of moisture getting trapped under it. The other is the bottoms of the door panels; usually when they’re flapping in the breeze like these, the bottoms of the doors are bad.
I suppose out there, you can just grab a sheep from the field, skin it, and slap it on the interior.😄
Wiring is probably shot from mice chewing it and the interior “fragrance” is probably enough to burn your eyes and nose.