Jack mounts inside, then there should be a black plastic cover that goes over it, held by 2 spring clips like the ones holding the battery box cover.
I was told to wrap a ratchet strap or similar around the outside of the case when the jack is installed, because if the cover opens up it can kind of ruin your day.
edit: I leave the jack handle and stuff sitting on top of the jack inside the case. With the strap around it I'm not concerned about any of it falling out.