The lack of sheet metal at the rear of the car isn't laziness. There is actually an advantage here. The lack of any obstruction at the rear of the car allows air to escape from underneath the car as easily as possible. As the low, sloped nose at the front of the car pushes the air up and over the deck of the body, the air pressure differential is increased, creating downforce. It is the same reason the rear bumpers on Nextel Cup cars are so high.
It can be difficult because there is so much body roll, but you should try to seal the sides of the body against the racing surface as close as possible. This is especially important on the right side of the car so that air will be pushed up and over the body instead of allowed underneath while you are sliding through a turn. To do this, you may want to try to use a piece of flexible plastic as a curtain underneath the rocker panels so that it won't get broken off if it does contact the track.
If you race in the crate motor classes, the rules will often allow a larger rear spoiler than normally seen in the Super Late Model classes. Take advantage of it. It may look odd at first, but more is definitely better here unless you are racing on some dirt superspeedway that's bigger than a half-mile.
The most important piece of aerodynamic equipment on a Late Model is easily the rear spoiler. Many racers prefer to build in a little insurance by fabricating a "tearaway" spoiler. It is essentially a standard spoiler split into two sections, one of which is a small piece-usually 12 inches wide-on the right side of the car. That way if the right-rear corner of the car scrubs the wall, the tearaway spoiler can rip off without sacrificing the entire spoiler. "But the tearaway spoiler is a bit of a crutch in my opinion," Richards says. "If my driver needs it because he is constantly running into the wall, I believe I'm going to have a little talk with my driver."
Also, notice the increase in angle at the top of the spoiler. This is known as a "wickerbill," and although it adds a large amount of drag, this vertical portion of the rear spoiler causes air to back up over the rear portion of the car, significantly increasing downforce.
Notice the rear-quarter window in this Late Model is only a decal. Clear Lexan also works well. If your rules do not specify, try making the right-rear quarter open so that air can move through it and contact the spoiler in the turns, while keeping the left-rear quarter window closed (either by not cutting a hole or by using Lexan). This actually catches the air moving across the car and pushes it toward the spoiler. This works better than having the right-rear-quarter window closed because it only adds downforce on the right side of the car, and body roll already puts plenty of weight over the right-side tires. Often, the rulebook will say you have to treat both quarter windows the same. If that is the case, keep both closed.