How do you add lava in an interior? I can't for the life of me find any tutorial that covers it, if I'm just not looking in the right place, I'd LOVE for someone to point me in the right direction.

There are six files in the activator tab;

in_lava_1024
in_lava_1024_01
in_lava_256
in_lava_256a
in_lava_512
in_lava_oval