I've had my Getaway for 8 years. After the first season, I thought about doing the same thing. It's fine when I am solo but when the family (wife and 3 kids)comes along they bring a lot of stuff. Anyway, I never did it. The storage coolers that are in the hulls from the factory are a molded part of the hull. My concern was if I cut out the factory storage coolers to add a bigger drop in liner and hatch or just added new storage to the hull someplace else (forward of the main cross bar or near the rear cross bar), I might be compromising the structural integrity of the hulls. Not to mention, if not sealed well, if you capsize the hull could fill with water and make righting the boat nearly impossible or very difficult to sail once righted with one hull half filled with water. You'd want to keep a bilge pump on board for sure.
I did add some 6" deck plates to the hulls behind the rear cross bar with drop in hobie bags for some safety/emergency gear. I felt the smaller opening in that location was not going to compromise the hulls and much easier to ensure a good water tight seal. Also, I wanted access to the inside of the hull by the rudders for maintenance/repair as one of the rudder pintles needed some attention. Certainly not the large storage area I wanted but at least the safety gear was not taking up space in the coolers that were used for other regularly used items like phone, flip flops, anchor, sunscreen, bungies, etc...
Please let us know if you end up doing it. I'd love to know if it works out.
This thread has a link in the first post to the hatches from West Marine I was thinking about using. They are the 13" x 30" box.
https://www.hobie.com/forums/viewtopic. ... it=storage