Rookie questions about my boat

[crsavage1]

Attached are pictures I took underneath the cap. Not sure I can tell much, it just appears it is one piece rather than a liner? I don’t see any through bolts or screws other than the screws from the rub rail coming through. Also took a picture of how I imagine you would cut the floor but question the vertical pieces. Are these structural that go down the hull to the other side? I imagine you cut around them as indicated?