here is the solution, ive been exchanging PM's with some1 who has just done it
buy a normal immersion heater, this guy got his from a plumber, it was 1 he had from a copper tank he had changed ( paid 10 quid for it )
it was then painted with a " engine paint " which is ok for heat upto 300 degrees, its a ENGINE ENAMEL, this bit was my idea, dunno if it works or not, but cannot see why it wont
this our guess would stop the "pure water " eating into the element ( for 30 quid you could change it every winter anyways, and you would only need it for a couple of weeks a year, just remmber to take it out when you are not using it, this would prolonge its life)