As I mentioned previously, I'm using the tracks from the model 1941 kit. They are made of Dragon's DS glueable styrene. I'm using Tamiya extra thin cement to glue the tracks. They are a tight fit on the tank, resulting in slightly bowed tracks around the return and drive rollers. I tried stretching them, but you have to be careful because they do not stretch evenly. Still you can get the tracks to settle down nicely on the wheels.
Here I'm using toothpicks to increase the amount of sag between the road wheels. It just takes a small application of glue where the tracks meet the wheels, and the sag remains.