I've got LOADS of seed I want to germinate... LOADS LOL... and I was up in my little greenhouse today and it was HOT.. getting up towards 27-30 degrees (must take the thermometre up to find out exactly how hot it is) at midday. How successful do you think germination would be with day temps getting up around this high and night temps falling below zero? I've got seed germinating inside the house at the moment on a small heat pad I have, but if I could do it up in the greenhouse I could do them all at once. I haven't built my hot box yet...

Sorry to say, but if the night temps are hitting zero, you'll lose the lot...You'd probably get away with a drop into the high teens at night (and it's often recommended), but I don't think any seedling will take much in the single digits....