DO NOT SAND YOUR BACK GLASS!!!!!!!!!!! When u put the tint on their its going to magnify those scratchs the tint will go over the defroster lines, just fine .......

PS: I do window tinting everyday and I'll just say that u could probably figure out how to do ur side glasses but you'll never figure out the shrinking of the back glass, if you really want to save money do the sides yourself and get the back glass done, let me know if u need a quote and good luck..........