Are you thinking of this box on Sea Wolf? It's not exactly a cooler, but it's the first thing that came to mind because it's custom aluminum and pretty slick!
One note is that if you have a single/main engine you may need a slightly different design. I have a board across the top of the splashwell (picture a much less cool version of just the top of the one on Sea Wolf) and I needed an "inset" cut to allow the engine to tilt (Sea Wolf has twins, so they tilt up "smaller").
Edited to add: Here is a photo showing my much-less-worthy board, but it does show the "nibble" needed for tilting the single/main engine (of course some singles may have smaller cowlings - my F80's doubles as a two-person lifeboat ). You can also just see the little "bridge" over the splashwell that I made following Two Bears' excellent idea. (Thanks Two Bears!)