Yes, the fridge being by far the main consumer can be run directly from the aux battery via a simple fused Anderson plug connection, the starter is isolated. Or, you could use the output terminal on the Smartpass, starter is still isolated. Pros and cons of doing this though. Pro is, the fridge is powered directly by the alternator when on the move leaving the 250SE to correctly charge the aux battery faster and without the interruption of the fridge cycling on/off, which can continually knock it out of the preferred charging regime and back into bulk mode. The con is the fridge load will be cut if the Smartpass detects the aux battery voltage dropping below 11.8V, or thereabouts. You may not notice the fridge is off, say you've left camp away from the vehicle beach fishing all day - disaster strikes and you come home to warm beers! It'd be prudent to wire in a cheap easy-to-sight digital voltage readout for the aux battery to give you at least a rough guide on SOC. Best viewed after the fridge has cycled off so the load doesn't skew the voltage. Stick the chart attached below somewhere nearby for quick reference. EFBs behave similar to AGMs.
If your fridge has low voltage cutoff you may as well run it from the Smartpass thereby letting the 250SE do its thing more effectively while on the move. If the fridge doesn't have volatge cutoff built-in you might want to run it direct from the aux. This way in a pinch you can keep the fridge running below 11.8V, but once you see 10.9V battery damage accelerates. OK once in a blue moon but best avoided where possible or the cells start turning up their toes.
Don't rely on the % display in the infotainment unit to monitor the battery/s while camped, it's likely far from accurate.
Until I have the vehicle and can suss out the wiring I'd just be leaving the roof outlets as they are and running a couple of LED camp lights from the starter. It's the same EFB 105Ah battery (think AGM) so should handle small loads like that no problem, as long as it wasn't 50% when you rolled into camp. You could add a 2nd voltage readout to the starter. Worse case you carry a compact jump starter for justin'. I have the Gooloo GT3000 which starts my 3.0L V6 Jeep no problem. see attached.
