A large chest freezer works well as an ice bin, use ¾" plywood for the top with cutouts where needed. good to make it two pieces so it's easy to bucket the ice out of the freezer/ice bin. Ours is in an old utility trailer outside, only slightly better than a roof over it with no walls. It gets hot in the trailer during the summer even at the coast, so we keep the side door open and the back doors slightly open. Having a large freezer to keep bagged ice in would be ideal but if the bin is large enough you can get by without the extra freezer for ice. Don't plug the chest freezer in, it'll just make all the ice into one big ice block. Old chest freezers should not be difficult to find, I paid $25 for ours but that was probably 8 to 10 years ago.
It's really nice to be able to get the boat (or the truck) close to the ice bin for loading up ice, esp for a tuna trip when you're loading 500# of ice in the boat. One of the few times it's easier to have the boat on a trailer rather than moored. For moored boats, at least in Newport, going to the Community ice plant would be much easier and while the cube ice works well, the flake ice works better and is colder, much colder. It's also got some salt in it so it cools the fish better too (lower melting point). I think most of the types of ice cubes world work about the same (smaller would be slightly better) except for the hollow cubes, I would not buy a machine that made hollow cubes.
As stated above, make sure you have a good place for the rinse water to drain and also the melt water.
If you have a large freezer or two to store bagged ice, then a smaller machine will work IF you have the time and dedication to bag ice often starting in early summer.
ron m