Where are you camping that you can't find sites?
Over the last 7 months, we did a big circle from Michigan, to Utah, to California, to Texas, to Florida back to Michigan.
Only time we had a minor issue was around spring break in Florida, there was a week where we ran into a few parks that were booked out but even there is was just a minor hassle of calling around to find a place with vacancy.
In the snowbird areas, we got some great deals as all the Canadians are stuck in the north and the parks are half empty.