[Destroyer]

I used a combination of tools to cut the deck. As you can see in the pics several places I went further than the corners with the cuts. Those cuts were made using a circular saw. Then I wised up and started using my multi-tool (http://www.harborfreight.com/power-t...ool-61219.html) to make the cuts into the corners. Much neater without the overcut of using just my circular saw for the cutting.

Yes, the middle round hatch is right over the fuel tank sending unit. Not really sure how much room you would have with them removed or out of the way, but it's not a bad idea to empty the tank as much as possible, remove the fuel lines and sending unit and try with a HAND pump to suck out whatever debris may be in the tank. Orientate the boat so that it's slopping towards the bow so any debris will naturally flow/move towards the pick up sending unit holes.

Finally, are you SURE that your vent line is clear? An insect or something could built a nest in there. I recall somebody in these forums a few years back had a similar problem with their ball collapsing and it turned out to be a mud wasp nest in the vent line. Take a electricians snake and run if from the tank to the vent cover and make sure it's clear before you go into something deeper. K.I.S.S. it first.