Pub stopovers are a great alternative to campsites for overnight motorhome parking. They are not 'campsites' though so should not be confused. They are merely pre-ageed locations to park and sleep overnight whilst on your travels.
In Europe there are thousands of 'Aires' which are specifically designed for the motorhome traveller. These are official parking areas for motorhomes to stay for a limited period so, again, they are not to be confused with campsites where extended stays are possible and are of course paid for. The UK does not have any proper system of 'Aires', preferring to make overnight motorhome parking as difficult as possible it seems.
So an alternative is to use agreeable pubs' and other interesting business's carparks.