We have done quite a bit of travelling in our old Bongo and now the motor-home around Scotland over the past 5 years. On the way up from Blackpool we usually stay at the Loch Lomond pier carpark at Tarbet ( luss - Google Maps). A bit further North after Tyndrum you could stay at the Bridge of Orchy, over the bridge behind the pub. Again further north on Ranoch Moor behind the Kings Houses Hotel, for that one you drive North past it for about 1/2 mile and then a sharp right towards the Hotel. There is usually wild camping tents there as its an official wild camp for the West Highland way ( as it is at the Bridge of Orchy).
Hope that's a start for you, enjoy Scotland, its great !