This might be of interest to you, we travel mostly France and Spain for about 3 months of the year. We stop mainly on aires which are mostly free or up to 10 euros per night, most european countries have them, France over 9,000. Most have basic facilities fresh water, tank emptying.
This is the website I use, https://www.campingcar-infos.com/index.php
Go to ‘aires camping car’, then ‘chercher une aire’ comes with all of europe pick a country and go from there.