Based on your boat I'm assuming you are replacing a full size, 120V fridge. We have almost a year with our new LG and have not had any hint of rust issues. Granted that's not all that long in the grand scheme of things but we've spent a good deal of time in salt air environments that would likely have tested it.
For what it's worth, the fridge itself has been terrific. Our choices were limited based on measurements but we've been very pleased so far. We got one with the door-in-door configuration which, for us, is a nice feature for a boat. You can reach in for a beverage without opening the main section of the fridge and letting the cold out. I know, not that big a deal, but something does feel good about it.