Rick the size & shape you mention sounds very similar to the rear hatch on my new Resolute which has a 25" beam. I made my inner lip for the hatch out of wood & put a layer of carbon fiber cloth on top - more for esthetics than anything - the lip extends under the deck about 1.5". Seems to deal with the strength issue - I do recommend you make sure your hatch cover fits very well. While playing around without the hatch cover on, I found the two inches wasn't much protection from water getting in. bye the bye - the size of hatch you've described is perfect for a large dog - which is why I made mine so large in the first place. cheers..ian