If i ever get to that stage i intend to use Raychem Winterguard
http://www.traceheating-cables.co.uk/wintergard.html
I have it installed on my water pipes(Caravan) and it produces a uniform heating of the covered pipe ect, same principle as weld preheating but a lot lower temperature. No idea of the cost but i have some left over from doing the caravan plumbing.
Regards
Mike