Using a spray bottle is a good idea but I wouldn't use it in this case it will be to slippery even with the smallest amount of detergent and you'll be heating it up for ages, also any detergent leaves a slight film if you have to use it use bio degradable, the graphics aren't that sticky until you apply pressure down on them, best thing to do is line up the longest straightest edge and maybe a screw hole cutout and just lay it on the plastic don't worry you can lift and shimmy the vinyl around a bit. Just move it around till you think it's lined up and then from the biggest flattest part start scrapping it out working from middle to edge, use even constant pressure. And yeah use a heat gun to twist or stretch if need be. Then once on heat it all down and go over any contour to be sure. I've apply my own graphics from Justin and its a piece of piss dry, just remember once in position scrap out hard if you don't you'll get bubbles, I've been a sign writer for over 8 years now and have stuck vinyl to just about everything the biggest thing is confidence, it's not that hard and heat gun is a savior. Good luck