Clorox! Buy a sprayer from walmart that is made for clorox. They make a couple of gallon sizaed sprayer specific for bleach use. I mix mine about 50 - 50.
Spray it and clean the rest of the outside and then rinse it out. Done. You can even spray it in your live well and rinse it out (it will not harm your bait the next time you fish). The truth is bleach is great for cleaning the floor of the boat also the only problem is after a number of uses it can remove wax. Same with where you clean fish, clorox! Why do you think on CSI they show the bad guys suing bleach to get reid of dna evidence. You can even spray it on chunks of fish and flies won't come around, period. I don't know what it does but it rocks.