Nice rig! Glad you could answer your own question.:sombrero:
I've been looking at the product you have linked to(the 275 amp product). It is kind of neat how it will use both batteries until they both reach 12.2 volts, then disconnect the engine battery from auxiliery loads as long as they are wired to the Aux battery.
The only issue I could see with this is that a battery, well rested, reading 12.2 volts would indicate that it is 50% charged. Starting batteries really do not like being drawn down to this level on a regular basis. So you might be replacing the starting battery more often than you like. But depending on the load applied to the battery especially by the cycling of a compressor fridge, 12.2 might be reached before the engine battery is really down to 50%.
I don't know that when the engine battery's voltage recovers above 12.2 when removed from the load(and it will), if the product will parallel the batteries again.
You could negate this by using an oversized deep cycle or dual purpose as your starting battery.
One other think I'll nitpick is calling the Dual battery LED remote device, a monitor. It is a simple voltage monitor, not an amp hour monitor. While Amp hour monitor give a fairly accurate reading in terms of State of Charge. Voltage monitors can be very misleading if not just outright wrong.
A rested battery, one that has not had any charging or discharging currents applied, for anywhere from 4 to 14 hours, can yield a fairly accurate state of charge by a voltage reading.
Just after running the engine, the batteries will have a surface charge, and a simple voltmeter will read 12.8+ volts for many hours afterward even under load, despite the fact that the battery could still be at or below 80% state of Charge.
For example, after a couple of cloudy days and much Laptop usage, my batteries were drawn down to 78 amp hours from full. After a full day of sun, the amp hour monitor read I was up to 18 hours from full, yet my current battery voltage, after using 30 more amp hours since sundown is still reading 12.8. This is under a 4.1 amp load.
The batteries according to my Amp hour monitor are at 78%, 51 amp hours from full. Yet the voltage is still 12.8.
Having only a voltage monitor reading 12.8 volts might trick me into thinking the batteries are still nearly fully charged when they are far from it.
I'm sure the product as designed and sold will fulfill it's purpose of allowing you to always start your vehicle.
If you are concerned about maximum alternator recharging, and accurate battery state of charge monitoring, then that product is lacking, and expensive.