Google maps and street view. Can be more time consuming than using an app, but has helped me find out of the way spots many, many times.
Whilst its great that apps are allowing sharing of info, they do honeypot people and inevitably, some spots soon become popular. Previously quiet places appear on an app and then there are always vans there. Before long a no overnight parking sign will appear. I know I sound like I am wanting to keep places quiet or exclusive, thats not it, I just worry with such a rise in van sleeping that it will become unsustainable.