Edinburgh lies on the southern bank of the Firth of Forth.

City of Edinburgh Council

Long/Large Vehicles

Vehicles should fit their wheels within the markings of the bay they are parked in otherwise they may receive a parking ticket. It doesn't stipulate motorhomes. It goes on to say that you can park on yellow lines for 30 mins for loading so it is clearly aimed at vans or trucks.

Dunbar - John Muir Country Park - The signage initially gives the impression that there is only height-restricted parking but following the road around past the barriers, there is a high vehicle and horse boxes designated parking area with space for eight or ten vehicles.
Parking is £2 all day. And it's a brilliant spot for walks. PY.