Make sure the freezer is placed on a flat, level, and solid surface.

"Level, eh?"

And this little tidbit...

Do not turn the portable freezer upside down, on its side, or 45° or more off level.

And there is this:

This portable freezer should not be placed in a built - in or recessed area. It is designed to be freestanding.

Maybe this ISN'T the right unit for a boat...