Fabric softener sheets work for me! You can use new or used sheets and I use the cheapest sheets I can find!
Just wet them with your wash water and wash away.I use a little Dawn in the wash water also. Once you do the initial wash with the sheets it is easier from then on! They leave a coating on the front cap that makes it easier to get the bugs off from that point on! Have had no problems with my decals at all. I have read from other posts- not to use waxes on the decals- that came from the decal manufacturer!
I even use the softener sheets on the front of my TV and the wife's car for the bugs. It works like a charm and it's easier to get the nasty little smashed critters off from that point on! I use Awesome on the front area below the cap to get the tar and etc off that but have never used it on the cap itself.
Try the drier sheet approach and I think you'll be pleasently surprised.