How do you mold a body kit to a car with fiberglass?

Since most of the time the body kit bolts on but does not fit correctly you must make it fit. Most people use fiberglass and build up the areas that need to be filled. Once you build it up so that there are no gaps in the seams or very little gap then your done. You must get fiberglass sheet resin and hardener after applying let it dry and sand. if you dont sand and add on top of an uneven surface it will build up uneven the dry time depends on the temp and how much hardener is applied i usually just let it dry overnight since i work at night.