This thread and @4RunAmok post has been very helpful. I'm following is advise and using a Group 27 starter battery on my 5th Gen and keeping it topped off via solar. Still have to decide whether to mount a 100 Watt or 160 Watt solar panel or go in for a 100 Watt or larger portable unit that has the flexibility to be placed optimally and angled. @4RunAmok , in your experience is the renogy suitcase with its semi rigid case robust enough to tie down on a roof rack for transportation or does it have to be inside the vehicle? If I go for their portable option I'd consider the one without the PWM as I'll have a permanently mounted MPPT in the back of my rig.

From my research on portable devices, if one is willing to spend a bit extra and go for quality stuff one can get something that will last a lot longer and charge a lot faster via 12V DC. For example, the ARKPAK 730 can be paired with a 50 or 100 Ah lithium battery (or a Group 31 AGM) and can charge from your starter battery (via Anderson plug) at 7 Amps.