I talked to the owner of an RV park not long ago, and he said that yes, off-season travel is way up. He thinks that compared to the recent past, many more folks are retiring in good health and are able to travel into our 70s and beyond. He said that 30 years ago, the typical person of 70 was not up for the rigors of RV travel.
So the off-season crunch may be an unanticipated side effect of better healthcare, better pharmaceuticals, and better dietary habits. We have the same number of campsites as before, but more RV travelers.
Not sure if this is true, but it sounds like it could be true. I certainly see many more reasonably healthy seniors cluttering up my local surf break than I saw 30 years ago. (Note -- I am one of the seniors.) ;)