Its been almost 2 years since I did the conversion. I thought about hooking up the defroster but I'm actually glad I didn't go through the expense or trouble. I don't recall the back glass being fogged up more than once or twice and the cabin of the car is so small, the dash vents don't take long to clear everything up.

As bosshog says, the labor charge for a shop to do it is understandable. Not only does it take a while, but alot of that time is spent with your body contorted in back numbing positions. But that being said, I'd do it again in a second.