Fridge 0.2
Re thermal mass.Could you not section of the part of the freezer with the cooling elements, and fill with water.
You could then cool that below zero increasing the effectiveness of the thermal mass.You'd also get some freezer space into the bargain.The only issue would be passively moving cold into the fridge proper.
I know greenhouses use wax cylinders that expand in heat to open louvre vents, I wonder whether something like that would work.