To make gatling use the JAVA_OPTS environment variable for ssl settings, copy this into your build.sbt

build.sbt

// Copy JVM ssl settings to be used by gatling
val systemProps = new SystemProperties

javaOptions in Runtime ++= Seq(
  mirrorProperty("javax.net.ssl.trustStore", "gatling.http.ssl.trustStore.file"),
  mirrorProperty("javax.net.ssl.trustStorePassword", "gatling.http.ssl.trustStore.password"),
  mirrorProperty("javax.net.ssl.keyStore", "gatling.http.ssl.keyStore.file"),
  mirrorProperty("javax.net.ssl.keyStoreType", "gatling.http.ssl.keyStore.type"),
  mirrorProperty("javax.net.ssl.keyStorePassword", "gatling.http.ssl.keyStore.password")
).flatten

def mirrorProperty(src: String, dest: String): Option[String] = {
  val formatProperty = (key: String) => (value: String) => s"-D$key=$value"
  systemProps.get(src).map(formatProperty(dest))
}