My Norcold that uses 1/2 gallon per day is 12 cubic feet, so twice as big as yours.
People often challenge my 1/2 gallon per day--I know I was surprised when I first calculated it. But I gathered the numbers while boondocking for weeks at a time, and they're not complicated by use of propane for hot water because we use solar for that, and it's not cold so there's no furnace use, and nobody around here is a cook. So 1/2 gallon per day it is.
EstorilM? We've been dragging an estoril blue M-Coupe around for 14 years of fulltiming. It's beat to hell, and that's just the parts you can see. :)