My first iteration with the Zodi Extreme was using it as it is sold, with me providing the air pressure via the hand pump to drive the hot water out of the can. I just pumped it up until I couldn't pump anymore, don't know what the PSI was at the time. Then one of us would go and take a shower inside the ATC Bobcat. When it was time to do a second shower, the second part of the tank of hot water, I did have to pump it up again, until I couldn't pump anymore. The shower head had an ON-OFF valve so control of the flow of water was done by the person in the shower. That was OK as the Zodi Extreme was only used every 3 - 5 days and I only had Popeye arms for a day or so.
After about a year of that I finally decided to buy a Vair air compressor for airing up the tires after going where that need to be done. I also purchased a small 1 gallon 150psi air tank and an air hose to operate some ultra small air tools that I wanted to take with me on trips. This package (Vair, air tank, hose and tools) are about half the storage size of the Zodi Extreme, pretty small, small enough to fit behind my driver's seat with lots of room for other things.
Then the light turned ON. I could use the air tank, with the compressed air at 100psi to connect with the Zodi Extreme, and no more hand pumping. Taking a shower was now a piece of cake with the modern tools of our age. The 1 gallon air tank at 100psi does the whole tank which is two showers, one for me, one for my wife.
Recently I bought into the Ryobi Lithium ONE 18+ volt battery idea with a couple of tools that are lighter than my DeWalt Ni-Cad battery units for when I need lighter weight cordless tools in odd locations. Turns out Ryobi has a nice inflator/deflator for not too much $, so I may just get that, instead of the Vair, to power the air tank and thus the Zodi Extreme.