The challenge with this van is to have enough power to run a small fridge full time with available power for a bit of ham radio. So far, with the two batteries that came with this van, the system hasn't really been up to it.
In the last few days I disconnected both batteries that came with the van and attached a 150AHr battery I've been using in my shed's solar system. This has done the trick. Gone are all those deep dips in voltage when the fridge was running without full sun and it now looks much better.
Along the way I learned that the solar charge controller doesn't get on with the fridge. If I connected the fridge to the "load" terminals on the controller it would flash the load symbol which indicates a short circuit. I guess the initial inrush of the fridge is high enough to trigger that protection so I've had to connect directly to the battery. Fortunately the Waeco fridge has its own low voltage shut down so it won't over flatten and damage the battery.
The 150AHr batter is big and my plan is to mount it under the bed and remove the big battery box that rather fills the space behind the driver's seat.
All good fun learning about this but beware that batteries that come with campervans may well have been mistreated. The Arduino voltage logger has been a great tool for figuring out how the system is performing.
Power consumption of a fridge is dependant on multiple factors including: temperature difference between the air and the internal setting and temperature of liquids placed into the fridge. I've seen it work hard after having a full load of room temperature beer added.