Hiya Jan,
In response to what you said about cooling, to be honest I don't have a clue how hot they run, but as you said the contact area is small so thats why I made a close fitting coil and covered the whole length of the 900 to increase the area of contact, it maybe over kill or it may not.
But at least now its done I wont have to mess around with it again.
But thanks for your remarks.
Steve.