Never camped in the Cairngorms, but I do take my dog camping. Water is far more important than food for your dog, make sure to take enough for both of you, you might not find a handy wee stream if we have one of our once a decade dry spells.
I cut down an old sleeping bag for the wee fella to sleep on. He seems to like it, but I can guarantee he'll still try to crawl into mine if it's not zipped!
Make sure to keep all the vents open, even in sub zero temps.... dog farts in a tent are magnified tenfold on the smellometor.