I learned how to apply vinyl decals from a friend with a professional sign shop in a major city. After starting with a clean surface, remove the back side of the decal. Then use a spray bottle with water and a small amount of dishwashing solution (like Dawn) to spray both the surface of the rig and the back of the decal. While thoroughly wet and soapy, gently press the decal to the surface. The water and soap will allow you to slide the decal into position.
A plastic squeegee can be used to squeeze the excess water out of the decal and permanently affix it to the rig. use an Exacto knife or small pin to pop any bubbles you can't remove with the squeegee to lay them flat.
I've applied lots of vinyl graphics and this method seems to work the best. Good luck!
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