Yes, two different power sources, but not really more flexible.
Say you run out of Gas or the gas reg fails ... You will have no real alternative but to go to a campsite and use EHU as a 3-way fridge is so power-hungry on electricity, you won't be able to run off batteries OR from
solar for any significant period of time unless you did a significant upgrade of both - or you ran the van engine virtually constantly (which is not practical). So where is your true flexibility? Gas or EHU
If you run out of
battery power or the
battery fails, then ignore the fact the fridge has no power - you won't be off-grid anymore as you will have no lights, no water pump, no nothing. So again here you are
Battery (which you need regardless) or EHU.
Same difference really.... If you are out of the primary fridge energy source (
Battery OR Gas), you need electricity.
But .... the difference between a 3-way fridge or a Compressor Fridge ... if the gas was out or the
battery was low, by starting the engine to use the split charge to get power to the fridge, if you had say a 30A B2B, over half of that power will go to running a 3-Way Fridge, whereas less than a tenth of that power is needed to run a compressor fridge and the rest will go to recharge the leisure
battery. Now THAT is flexibility.
To put it another way ....If in my motorhome, the batteries were too low to run the fridge-freezer, I could start the engine and I would have put
enough power back in the batteries within 40 minutes for the fridge to then run for another full 24 hours.
Now IF there was a truely efficient dual-fuel Fridge that could use Gas and was as good on electricity consumption as a compressor fridge, that THAT is flexibility. but it doesn't exist.