I added a second battery in parallel with the original. They're both Costco / Interstate Deep Cycle Marines - nothing special.
I've got (2) 100 watt Renogy monocrystalline panels on the roof; the battery and panel combination has worked well.
You're lucky that Lewster is up in your part of the world; he's like the world's expert on Airstream solar setups.
"Between what matters and what seems to matter, how should the world we know judge wisely?" - E.C. Bentley, Trent's Last Case