I use a hair dryer for that, works perfect with no chance of melting/crinkling it.. i'm surprised you got away with the heat gun.. more patience than me :)
(i use a hair dryer at work to remove old shipping labels off packages.. works great.)
I did use the Heat Gun on Low temp.....Just a little of the silver color behind the decal game off. Think I can touch that up with a silver sharpie or light paint... :thumbsup: