Question for Jeff M (WA) Dual batteries

Utemad, yeah the system is pretty simple, I'm actaully going to "Mod" it again because I found a flaw in it while leaving the car in the garage for two weeks. The system currenty draws .5 of an amp to just hold the arrid open. This obviously is barley noticable with 210amp/hrs on board for day to day use but after two weeks it had noticably dropped the batteries voltage down. I'm going to fit "ANOTHER" switch to the dash near my Battery LED so that I can switch it from voltage sensed to ignition triggered.

So basically it works like this:

Bat A = Starter.
Bat B = Auxillery.
Both are 105Amp/hr 550CCA Calcium-Calcium Batteries (identical).

I have an Arrid Smart Relay (just a glorified 70amp Relay with a 2min delay after power has been applied).

These are all connected via 2g Cable in the standard format.

Now instead of triggering the Arrid via the ignition, I am triggering it from a simple LV Cutout that's running direct off the input to the arrid (so this is basically how the Redarc works anyway). The advantage is that I can switch between LV Cutout and Ignition Cutout via the switch on the dash. I also have a green Led on the dash that tells me when the batteries are connected.
I've set the LV cutout to cutout at 11.9V and cut in at 13.1v. You may want to set this a little higher, I have it low because my fridge draws 8-10amps and causes a fair whack of voltage drop accross the system so this compensates for that. But Even at 0c the diesel will glow and start after it's cut out at 11.9v off one battery. It made a HEAP of difference to run times, because not only is there more usable battery power the load is spread accross the two batteries for the majority of the time. In fact it basically doesn't cut out during the winter overnight stops, during the summer it will because my crappy "tim the tool maned" cooler runs at about a 50% duty cycle at 8-10amps!! ARRGH!. But it works, beer is cold, that's all that matters. ;-)

I reckon you could probally mod your Redarc to do exactally what my system is doing, I've never had a close look at the red arc but surley you could adjust the in and out voltages?? Then just run a small relay off the ignition so you can overide it back to ignition switched. That way when you not camping your not coping with the 500ma parasitic load that the Red Arc will draw while open.