So IF it was full amperage at the campground (not everything is as advertised), it would be more like 6.5 hours. Still not acceptable. However, your car will charge faster the first half than the second half. If you charge to about 50-60% & then stop again at another campground, it will be less than 6.5 hours total. Remember, at the last place you charge before your destination for the night, you only need to charge enough miles to get the next leg.
Stop to eat, pick a place where you can plug in. Need to stretch your legs? Same thing. My last roadtrip pretty much used 70 amp HPCs, but I've had others where I relied on both 30amp and RV parks.
If you can find owners along your route, then you might find HPCs to use. But most of us are happy with NEMA 14-50 service. Have you searched the different sites like recargo.com, plugshare, etc?