I don't have experience with refrigeration but I wanted to note that Practical Sailor did a review last year on several kits to convert an existing icebox (err, ice melter, in Catalina parlance) using 12v systems that are water and air cooled. Sadly it does require a subscription to view the article on their website.
I do recall the article mentioned that all the kits they reviewed use Danfoss compressors with variable speeds to better manage power usage. Thus you could run at full power when power is readily available, and kick it down a notch or three while on battery, though with less cooling capacity. Good luck! David [Non-text portions of this message have been removed]
