Brass Monkey were mentioned by probably "The Guy" when it comes to 12 volt fridges here Shitney for their reliability & value for money ........ he just doesn't see any come in for repairs . The downside I could see is that they need to be kept relatively flat when operating (<15 deg) which would be an issue in a boat .
Ebay fridges would be a real roll the dice kind of thing though - I'd really want to research the gear before I hand over hundreds of dollars so If I go down the path of buying a fridge for the boat - I'll probably spend the coin .
Chris