I'm a bit of a nerd, and I was an OTR trucker for a while.. so here's a suggestion of a few things to consider.

Firstly, A permanently installed charger. The idea here is that you can plug in, and not worry about running the battery down by running accessories. You could run your radio and lights, and your battery will still be plenty strong to start the engine.

Secondly, Waterproof AC ports. One would go well in your wheel well for the charger, but putting another somewhere hidden on the rear underside would allow you to power things like a laptop computer or a space heater while keeping your car shut and sealed.

There are different styles of both of these things that offer different advantages. This version of the port offers two outlets and This integrated charger supports charging two separate banks at once if you were considering a second deep cycle battery for something like an inverter.

Although, the Soul doesn't have that much free space under the hood. Depending on your power needs, you might be better served by a solar generator or maybe an oversized powerbank for those times when outlets aren't available. I figure the flat roof of the soul is ideal for solar charging in a pinch.