nope wouldn't peel, I didn't use a heat gun, just a hairdryer
I never used water either. the issue is making sure you don't get bubbles under the wrap.
I folded it - so for the sides I left quite a bit under the a pillar I think its called. and then just put them back over the top to give a clean finish. for the back of the roof you just have to cut it and fold it in the gap between the boot lid and the roof. the front, you can hide it under the rubber windscreen strip!