Removing rub rail?

[jetroc0088]

Well, not actually removing, but it almost got tore off in a nice size swell. I have the aluminum rub rail. I took a section of it off to try to repair it and put it back together. When I got it off i noticed that the top half of the boat, the deck, or the white part sorry not sure what it is called exactly, is not completely attached to the hull. Is this how it is supposed to be? Or, is it supposed to be sealed? Or, do the screws in the rub rail act as the bond for the top and the hull?

I am pretty nervous about this part, as I do not want to mess something up.

Thanks,
Chris