I worked summers at WCCW in Traverse City, MI, a very tourist-based economy at the time. While there was some "summer advertising" there was really no huge increase in radio revenue from tourism. There was a "pitch" to advertisers about tourists, most of whom came in cars, listening and hearing ads, businesses knew that the most effective media was the collection of tourist newspapers, magazines and the like that were handed out everywhere.
I can't see that this has changed much over the 6 decades since I worked there! (except that now tourists can type in "steakhouse" and click "Allow to use your location" and, voilá, a list of 'em.
And the year-round population of Grand Traverse County alone is creeping up on 100,000 (and much higher in the summer; fun fact: TVC is the third busiest airport in Michigan after DTW and GRR; it has jumped LAN, AZO, FNT, and MBS over the last decade or so)

