Catalina changed the inner hull on the model 3 to remove the "tunnel" and add the water proof hatch. With this change the size of the opening is different. Afew years ago I did alot of investigation on how to add a waterproof hatch on the model 2 and gave up. There are no "off the shelf" waterproof hatches on the market that will fit and give you an opening that is large enough to get things thru. If you want to remove the "tunnel" you will need to fabricate somthing yourself and it needs to be water tight.