I've replaced all the festoon bulbs in the interior with LEDs. You can get them with varying amounts of LED elements (up to 24, I think) to modulate the amount of lights you want. Your current drain while camping will be drastically reduced.
I've also installed a few extra fixtures in my Westfalia interior. There's two that are actuated by momentary-off switches, one over the door of the coat cabinet and the other at the back of the head-banger cabinet; both are actuated by switches in the sliding door and rear hatch respectively. I've also installed a bank of reading lights over the rear seat. All these used the same fixture as the front cabin light. And I procured another of the three-bulb fixtures used in Westfalia campers, and installed it over where I've set up a stove. When I have them all on, I've got the brightest-lit bus on the campground.