I'd agree as long as the dog generally doesn't mind being left alone and has full roam of the boat and assuming it's a fairly sizable boat relative to the size of the dog.
Boats do get hot inside during the summer BUT you will often find the floor is usually considerably cooler especially if you have tiled or laminate/wooden flooring. Lay down on the floor on one hot day and see for yourself! Quite surprising. Dogs also have sweat glands on their paws so this is a good combination.
My dog's vet told me that most young/middle aged dogs have very good bladders and can hold it much much longer than humans can, without discomfort. While it's always good to let dogs out as much as possible, it's worth bearing this in mind. Of course, puppies and older dogs will need more attention in this regard.
I'd also recommend a dog camera that can be fixed to the collar. This way you can keep an eye on your dog remotely as long as you have internet access.
My boat has port holes at the rear where it is considerably cooler. If heat is a concern, the more port holes the better. I really wish my boat had port holes and nothing else.