What goes in the crack?

[hermco]

My first diagram was an attempt at showing your liner,the second was a diagram that attempted to show a typical boats liner. The carpet in yours might have been installed before the liner at the factory or a previous owner might have stuffed it down the crack. Either way the carpet should come out of the crack if you want to fill it. Or you could leave it alone. It's your crack and I'm not gonna tell you what to do with it.