I think other factors you might want to consider are what you are going to be powering with the vehicle off? Fridge, auxiliary lighting, etc.
Personally, I've been having pretty good luck with an Odssey group 31 in the oem battery position in lieu of a dual set up. I only use it to power my Dometic 75DZW. I have let it run for over 24 hours with the truck off, with no issues starting. There can definitely be concerns with that though, so I make sure to always carry a charged jump pack with me. Cost was a bit of a concern for me, which is why I chose to run a single group 31. Also, I second what Brett says about the voltage booster. You should definitely buy it now since he stops production sometimes, some of my friends have had issues trying to buy it. These deep cycles need higher voltage to meet its full service life. It's a much cheaper alternative to a high output alternator. I think I will still run a second battery down the road, just for peace of mind! Hopefully this helps, don't hesitate to shoot me a PM if you have any questions!