Well, I finally finished creating more space in my 26' Alaskan. First, I removed that big fresh water tank and replaced it with a 5 gallon container. We won't ever use 20 gallons of water anyway, plus we always have at least a case of bottles onboard too. Bought some regular hose barbs and threaded them in and sealed them with marine sealant.
Next was removing the ice box. There is tons of unused space in there. I built a raised floor so water could pass under and hopefully keep dry. It's easy to remove occasionally so I shouldn't have any problems. Then I built a shelf with a couple slots for the tank fill hose and sink drain. I also widened the opening by 3 inches all the way around which made it a lot more accessible. Built a couple doors for it with self closing hinges and filled it with rubbermaid bins.
The last thing I did was rivet two pieces of 1/4 aluminum channel inside the transom fish box to give me a 15" sectioned off area. I bought a plastic cutting board from Wally World and cut it to fit. Now I have a divided fish box that can be used for bait or whatever.