Real sorry to hear that progress was not as good as you had hoped.
You can't say you didn'y try. I have tried to help over the past season, but in the North it may just have been one of those years. Never having had use for a heater I cant really give you any advice on which one. But I'm afraid it's too late to hope for anything developing from now onwards. Saying that I have just started some beetroot this week along with potatoes and they will be grown in the pollytunnel and should be ready for xmas.
Dont want to rub it in but I need to get rid of my tomatoes before I can plant anything. Have boxed and frooze thousand's of maskotkas. Am now bringing two large seed trays full every day (approx 10lb). The neighbours are fed up with beans, so now I'm going to put them off tomatoes.
This ones for you zabado ..
http://i57.tinypic.com/2qbacgp.jpg .. better luck next year.