across the country a bit, but we have stayed with our motorhome in one of the picnic spots on the banks of Loch Earn near St Fillans. People were pitching tents on the beach for fishing.
Or another spot that is more open is around Strathyre area the lochs (I think its Loch Lubnaig) round and about have wide stretches of pebble beaches and we have seen people camping in tents and with campers there - its on one of the tourist routes but quiet. check it out on google earth
How far north do you want to go?