Not a dumb question.
So I have the Off-Grid dual battery set up as well as the Redarc BC-DC charger. You need the Redarc BC-DC charger if you are running AGM batteries because they need the 14+ volts to correctly charge the batteries. I am running 2 Odyssey Group 34R batteries. I linked them with 2 gauge oxygen free car audio wire. Literally have almost as much in wiring as I do in 1 battery. You can also accomplish the 14+ volts by purchasing the OV Tuner from Orange Virus and using a map set up that ups the voltage from the alternator. Yes, you can isolate the batteries which I have done with the Blue Sea ML-ACR. I usually have my batteries isolated unless I am charging the secondary battery.
Ive done so much research on this, if you have any questions, hit me up. I can send pics of my set up if you need. People on this forum are awesome and most can help. I started a write-up on my battery setup, but then life happened and I had to put it on pause. I will probably finish it in the next few weeks and then post it here.
If you want the Redarc BC-DC charger, let me know as I am not going to need it now due to the fact I am going to order the VFTuner probably tonight.