Greauxpete: In case your unit doesn't work out the way you hope. I'll offer an 'off-the-wall' idea. I'm good at those
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I saw in Home Depot what struck me as one of the smallest window AC units I've seen. It was a Toshiba offered in both 5,000 and 6,000 btu's at same dimensions, similar weights and prices.
Here are specs:
IF it fits in your fridge space, then would need to solve where it draws air from. Ideally, you want it to draw air from the cabin as far from the intake as you can.
But I suspect the area behind your fridge could draw air all the way to your head holding tank and maybe even gas tank. So the challenge would be if those areas can largely be cut off from circulation. If so, then you just need an intake vent to the area behind the fridge.
And you may need a condensation tray that drains to the bilge or to the shower sump.
Like I said, and off-the-wall idea. A lot more work, but a lot more cooling power.
Since its 110 volt, could install a 100 receptacle below the helm. It has the male end facing outside and a short female end on the inside of the bulkhead.