Swindon to Scotland -- suggestions for route ?

I got my vintage Eriba a year ago, and have been multiple short trips away- just me and my 2 dogs, and Ive loved the independence and adventure. This Sept Im thinking of a longer 2 week trip, and would love to go to Scotland - stopping on the way to break up the journey, and including galloway and Dumfries and Lock Lomand / Trossocks. Ive ear marked Garlieston Site as one to stop off, but I cant make up my mind for the route - ? Swindon --> Peak District --> Dales ---> Galloway --> Loch Lomand, and then where on the way back. Any suggestions for routes or sites to stop off at would be very much appreciated. I'd like to keep each journey to about 4 hrs maximum and stay a couple of nights before moving on.