This may be a dumb idea, but what about having a new drop from mines/wrecks that would be ammunition for the large gun turret in outposts. If a Leviathan spawns the turret would shoot in the direction of the Leviathan possibly alerting the player to when one spawns. Players would only see their turret react if they loaded it with the ammunition, the turret would deal damage contributing towards a prize, but not enough to significantly alter the rewards. The ammunition might even be used when the player is offline allowing the player to earn the minimum 1 reward even if they missed the Leviathan making it worthwhile to restock the turret daily.