I had the same question when I did my first cross country trip. What I ended up doing was planning my trip based on what I wanted to see.
I then used RVParkreviews.com to determine if there was a campground near by. I summarized the campground average nightly cost over 10 different customers and averaged their reviews over 10 different customers, all in a spreadsheet. I then made my decision based on #1-lowest cost #2-best rating. Once I determined my top two or three campgrounds at each location I started looking at maximum lengths and whether or not my dog was allowed. Not all dogs are allowed at all campgrounds, especially those mistakenly considered vicious.
Now I'm only at 34' on my 5er but I only found one campground that came close to not fitting. That was a state park on the California coast and we barely fit.
I've been on two cross country trips in 5 years and based on what I saw there are very few campgrounds, private or public where a 43' rig won't fit. Are there some where it will be a bit snug, absolutely, but not many where you just won't fit.
I think many people over think this issue.
Because we are not retired and only have a certain amount of time off work we push as long as we can on drive days. We'll do anywhere between 8-12 hours depending on what we are trying to accomplish. When towing with a deisel the drive distance is no big deal for me but is for others. Just stating our preferences.
