I don't have an answer for your question. People don't seem to like to talk about earthships around here much.
Before you decide to build an earthship, you might want to find a place to make a small retaining wall from pounding tires full of dirt. Mike Reynolds used heavy equipment to dig the dirt that was used in the tires. If you plan to dig the dirt by hand and pound it in the tires....you may find that YOU are the tired one.
I made a small retaining wall in my yard from dirt that i dug up and wheel barrow-ed over and pounded... 4 tires was enough for me. Not 4 layers - 4 tires side by side. Going up to higher levels without machines would add even more hard labor.
I may still use pounded tires as a footing for my next structure, but I'll probably use other materials for the walls.
Sometimes the answer is not to cross an old bridge, nor to burn it, but to build a better bridge.
I'm still a ways off from that mostly in the planning phase.
The tanks are actually part of an aquaponics system that I'm upgrading.
I'm pretty set into doing an earthship, I've gone away from cordwall since we did a shack like that and while we didn't build it to the highest standards its a tad drafty, and we used wood that had been seasoned for 3 years almost.
Looking at places up in the high desert in Arizona and I think an earthship will be perfect up there.