No you'll be fine; especially so if you arrive before 3pm, arriving late/early evening at a popular aire in peak season can be a bit of a squeeze for any size motorhome. All other times I doubt you'll ever have a problem
They can be a bit tight, we did 2 months in 28ft MH with 10ft trailer. Just take a look around and pick your spot with exiting in mind. On the smaller ones if you are not careful you could get blocked in by someone (without them realising) and sods law they will have gone out for the day.
We had more problems with camp sites, especilly those with trees in every corner.