Moshe, The best way that I have seen is to use a thermally conductive isolation pad between the rear of the transistor and the chassis. The pad should extend beyond the conductive part of the component so creepage distances are maintained.
The transistor would be held tight to the chassis by a type of "clip" that is non-conductive, which is screwed to the chassis above the component. Good luck! Edward Eszlari TUV Rheinland
