I look at it this way, just for numbers, say your PC and driving style get 8mpg and gas goes up to $8/gallon. That's $1/mile for fuel. Over the years, I have taken several trips that were in the 5,000 to 6,000 mile range. Those are 5 to 6 week trips. So about $1,000/week for fuel.
That's affordable if it's planned for. Yes, there are campground fees and those can add another $300 to $500 per week and again, they are planned for expenses. The rest of the costs, food and so forth are about the same home or away. So compare those costs to flying to a resort, paying the hotel bill, renting a car or paying a taxi, eating at a restaurant 1 or two times a day. Those expenses can easily be $5,000 for a 2 week vacation.
So, $5,000 for 2 weeks vacation at a resort or $3,000 for a 2 week RV trip? The only other choice would be to stay home and watch grass grow.
BTW, the 8 miles per gallon is driving at 70 and 75 mph speeds. Get off the interstate and keep to 60 mph speeds and I can easily get 20% better mpg. A good tailwind and I have gotten 11 mpg... Seriously.