is there any reason to not fill these spaces drawn in the following photos with fiberglass? my thought is it will help the roll out of dirt and other contaminates that accumulate in the boat and make washing it out easier. the only one i see that may need to be left open is the one in yellow in case the suction piece needs to be removed. along those lines if the suction piece needs to be removed i would assume major work is about to take place and cutting off the glass to access it will only be one more step. if any color needs attention please specify the color and a reason.
Do not fill in the yellow area. Those screws need to be able to be accessed for the intake removal, not the suction removal. I see no reason to fill in any of the areas you are thinking of filling in. Clean it up and keep it clean.