Don't be confused. I'M not going to install it. That would be sheer stupidity! I simply need to purchase it.
We are not here to spend your money; however, why not go to a trusted RV dealership and have them do the install of whatever will work best for you? I assume you are familiar with the power draw of a 12 volt refrigerator when the batteries are
not being charged. You probably need to know how long (really how short) the refrigerator will work on 12 volts when the batteries are not being charged. If your refer is old, it might be money well spent to look into replacing it with one that has a propane burner as they run days and weeks on one bottle of propane and will switch automatically with you flipping no switches when plugged into shore power. Many modern RV refrigerators don't even have the 12 volt only option anymore.