This is a big one. To make the panels flush, and flow together seamlessly, use a piece of aluminum flat stock or c-channel (as I'm using in picture). This is used to span across panels, and shows you where the edges of all the panels need to be. Hammer & dolly or shrink the highs down, and then move the edges of the panels to meet the aluminum. If you get this right, you will be able to sight down the painted car, and will not be able to tell where the panel edges are. And your panel edges will be thin. **the thickness and length of the aluminum will depend on how much shape is in the car.