I think 34' would be okay most of the time. Several years ago we had a 33' motorhome. We preferred state parks and were able to fit in most of their sites. Part of the reason was because with the 4' overhang in the rear, we could back in and fit in a 29' site if need be. We also didn't have any issue navigating the roads in the parks at 33'.
With the current 40 footer, we have to pick and choose which parks we can navigate and less sites available at this length, but we like the extra roominess in the 40', so we deal with less availability.
We do have a 24 footer that we use in older forest service campgrounds when the 40' just wouldn't cut it. I think you will be fine with a 34 footer at most campgrounds though.
