Cutting the ribs was one thing, but in this step you are at the point of no return. This van is going to be repainted one day so you will notice my lack of effort in protecting the paint. Sparks and metal debris may pit your finish if you do not properly protect it. That said, my paint was unharmed.

When using an angle grinder it is good to remain calm and go slow. The walls are relatively thin so it is important to cut at a shallow angle to prevent the grinder from snagging and denting the metal. Using a steady hand make your cuts just inside the pattern you drew in the previous step.

I am all for creativity and coloring outside the lines, but this is no time for that. By making your cutouts smaller than needed, you will be able to make the holes bigger with the flap wheel for a perfect fit. If you make your holes too big, you will need to call the body shop.

The large cutouts were done as octagons. First the long sides, then small diagonals in the corners. To clear out the corners I made lots of little vertical slits and cross cut those resulting in saw teeth.