No - not really. Just when you have to put heaters in many tanks then you very fast reach quite high wattage over all which not only costs heaps but also puts a strain on the cables.
The problem is not "the tank" Caryl its "all these tanks", hence the idea of heating the room rather than the tanks.
However since it is outside and cannot be insulated any more except with a bubblewrap curtain or similar I will have to insulate the tanks in such a manner that I can still get at them for looking, cleaning, feeding, water changes etc.
I thought some others might have solved these problems already?