On a personal not, I just don't buy that those plastic srews are as good as rivets. Mine are riveted, at least they are now(a girl i new put her heel straight through the middle of one of mine, breaking both the screw in cap and the housing) so I replaced the two that were screws when I fixed that one. At any rate, when I had things apart it apeard that the procedure you decribed is about what was done. Be carefule using a jigsaw though to use a VERY fine tooth blade. You don't want vibrations creating cracks in the top of your hull all around the area you are cutting. It might be better to find a way to do it with a dremmel tool. Also make your hole slightly smalle than it needs to be and use a rotary sander to make the port frame fit just right. Since this part must make up for the structural intergrety you removed by cutting your hull, it is best that it is as close to perfect a fit as possible. I've never created a new port hole, just replaced old ones, so someone may think I'm a fool for suggeesting this. But my boat does have those extra ports you are talking about, soooooo, I see no reason why it would hurt your boat to put them there. My only concern would be creating cracks with the vibration of a jigsaw. I've completely shatted 3ft pieces of certain types of plastic doing that, and I wonder (am afraid that) the hull kmight react in a similar way. So that very fine tooth blade is important if you decid eto go this route.