I'll probably end up building a little circuit something like this. Initially I'll just wire a thermistor in series and see how much heat it dumps into the case, I suspect it will be an unacceptable amount. The thermistor I've got in mind is this. My concern is that if the relay fails to close then power will continue to go through the thermistor and I wouldn't be aware of it slowly trying to burn the house down. The alternative situation where the relay fails to open should blow a fuse / trip a breaker on start up so I should spot the problem fairly quickly.

I'll keep this thread up to date either way though.