Yes, we used a heat gun. Takes quite a bit of heat to get it to bend, so much so that it will blister the plastic. I would not suggest doing it on the car. It seals with an O-ring, so makes sure you have a new one on hand when you remove it. You could also save yourself the work and buy this:
http://mrcmfg.com/catalog/product_in...roducts_id=258
Dan