Hey Dawn!
Come back and just plug back into our 110 outlet...problems solved.
First, fridge, the temp will vary with outside and inside ambient temps and if sun is on outside of the unit. A full fridge will actually hold a steadier temp. Variance in the fridge temp is the rule not the exception.
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Next the issue of solar and available juice to run your FWC. A caveat, I am not an expert nor have I stayed at a Holiday Inn. Sorry if this is a long missive.
With all the thousands of words spilled about "upgrading to a better controller" etc, etc....it strikes me that the issue is simple...you need to have a source of incoming juice that is stored until you use it and if the outgoing power is more than the incoming you will run out of power.
4 sources can provide incoming power: Solar panel , 110 plug-in, truck alternator and a stand-alone charger connected to batteries.
Potential weak links:
#1 Not enough solar input to match what you are using. Could be a range of reasons why; defective solar unit, not enough light on panel or you are using in excess of the solar input. I might note that a dirty solar panel can result in a dramatic reduction in out-put; clean you panel. How much light strikes the panel is highly variable and mostly impossible to mitigate all the time.
#2 Batteries are not adequately storing and releasing the incoming power in sufficient quantities to meet your power demands. Batteries are of insufficient size/aH or defective. Again, you may be using in excess of the systems capacity to delivery power to match you usage.
#3 You separator is not shunting power to your batteries while the motor is running; or, you alternator can not meet the demands of bringing up the charge on your vehicle and FWC batteries. I believe this source of input to the batteries is a limited source of power and of course is dependent on motor running time.
#4 Your FWC charging system from 110 is inadequate or not functioning to capacity.
I may have missed several variables in this synopsis but it boils down to energy in and energy out. Assuming that you are frugal in using the electrical energy if you run out then you need to either generate more juice [more solar or plug in to 110 or run the motor more].
Lastly for what it is worth, I consider an "improved controller" to not be an answer to continually lowering or lost on-board power. Empirically, if you run out of juice you need more input or you need to use less. If a controller is in fact controlling the solar to battery flow of power correctly then how close you are to being out of power is nice to know but not critical if you already know from experience your usage is exceeding the input. Even the "idiot" lights on the Zamp and FWC panels showing "how much charge the batteries still have in them" are merely a reminder to put in as much juice to your batteries as is possible with your system; then use less than that amount.
Oh, remember the Master Power switch must be on for solar generation of power to the batteries...at least with our Q4 system. We leave that switch on at all times since the system will then receive solar and 110 juice.
You are welcome back here anytime, the "kids" miss you.
Phil