Hippy,
Let us get back to the issue at hand. 1. You need to power your slide. 2. You need to power your emergency brake-away TT circuit. 3. You may even need to power some of your phantom loads while towing or perhaps need some battery power for an unscheduled stop.
These can be solved with almost any car battery. A marine battery would be better, a deep discharge battery would be best.
Twice, I have had to fall back on my battery, once at a campground where power was cut for a few hour for repairs, and a second time out West when the only available overnight campsite site was in the primitive area.
I general my battery gets very little use but it does happen, powering the lights, slide, awning and etc. is indeed handy.
There is nothing mystical here, it is an easy solution to a simple problem.
