There was a good diagram on another website, but I can't find it. I have seen all sorts of stuff out there. One way is set up like in the pic (not mine). Parallel to the levy that is in front of you when you drive in. Probably not a bad idea to angle your line of fire into the levy. There is nothing beyond for a long ways, although there is a road similar to the one you drove in on in the distance that you should keep an eye on. You can see it on the google maps. Just follow the levy from the parking lot south.
Others will go over the levy and then shoot into it. If you do that, be sure to offset the road in so no one pops up right above you. I don't like that way that much since you don't know if someone is going to come up to the top of the levy and you can't see the parking lot or anything.
I'm sure there are some other techniques out there. Please help clean up out there when you go.