These methods can be applied to mounting any brand clear or thin styrene body.  If you are using another brand, use reinforcing tape inside the body, and drill very carefully.  Other brands of clear bodies are not as strong and durable as Boss Bodies.  These methods also work on other brand chassis.  Artin chassis is the easiest to work with due to the flat, vertical side walls.

The side of the chassis has a vertical, flat wall. Use a drill bit that will make a hole which leaves adequate space on the top and bottom of the plastic to retain strength.

Drill slowly and carefully.  If you're using a brand other than Boss Bodies, carefully reinforce the body before drilling.   Make sure that you leave some space between the back edge of the chassis and the hole.  Center the hole vertically so that one side doesn't become weak.

Align the body to your liking and drill a hole to match the one on the car.  Some people use double sided tape to hold the body in place during this step.  If you use two-sided tape, drill the body and chassis together.

Put a screw in the hole and tighten it up gently.  Do not over tighten the screw as this can strip the hole in the chassis.  Installing this screw before drilling the other hole prevents the body from moving while you drill the second hole.

Drill the second hole with the body in place. Be sure that the body is properly aligned before you drill through the body and chassis, because this will make the body position permanent.  Repeat this process on the other side.

Attach Velcro to the inside of the body, close to the bottom edge (rocker panel) and in between the wheel wells on both sides.  Most hobby or craft stores carry Velcro with self adhesive backing.

Attach Velcro to the side of the chassis in between the wheels.  Do the same on the other side.

Align the body Velcro with the chassis Velcro.  Squeeze the body onto the chassis side pans to attach.

The nice thing about Velcro is that you can pull the side off a little and adjust body rake.  You should adjust the body position on a tech-block or track section because the front wheels usually push up when the guide flag is in a slot.