Which rather implies that all conditions of parking must be conveyed by a PbP service.
Not at all, they should simply have a sign visible from where the vehicle was parked that says "
no motorhomes in this car park" and that would suffice.
There are no national regulations about signage in car parks, so it's down to the adjudicator to decide if the signs are adequate, and my firm view is that most adjudicators would say that if the motorist was able to pay to park and there was no signage indicating they shouldn't, then no contravention is made out.