Have a look at the thread I started years ago in regards to the floor pan. I'm going to try and update the thread with pics of what was done to fix my floor pan.

In the meantime, have a look underneath the car at the pinch welds. Verts have extra bracing. Are the joints expanded with rust? Mine were and that was the major issue with my floor pan. The actual flat floor part was in excellent condition. The flat part is patch-able, the pinch welds can't really be patched.