As a result of his involvement in creating the Free Port, Gustav III became vastly popular among the members of its upper class, as evident in the spectactular celebration of his son (the later Gustav IV Adolf) in 1778.
Tänu oma seotusele vabasadama loomisega sai Gustav III Marstrandi ülemklassi seas tohutult populaarseks ja see oli ilmne tema poja (hilisem kuningas Gustav IV Adolf) auks korraldatud suurejoonelistes pidustuses aastal 1778.