Hi Morag,
We go to this site regularly. As Deborah says, the road isn't narrow, although it isn't 2 lane either, ie, you can't get 2 outfits passed each other.
If you met a car, on it's own, coming the other way ( which has happened to us a few times ), they will reverse and find a small space to squeeze themselves into, to allow you to pass.
The worst situation and probably the one you're worrying about most is if another outfit is coming the other way. When you turn off the main road into the entrance road to the site, you can see to the " elbow " in the road, about halfway down, so if you see an outfit coming the other way, you can wait until they come up or maybe just a wee reverse ( 10 metres or so ) back onto the main road. The " main " road is very quiet.
If there's nothing coming, you'll get to the " elbow " halfway fine and there's probably enough space at the elbow for 2 outfits to squeeze past each other.
So that leaves less than half of the road to be lucky and not meet another outfit. I'm sure you'll be fine.
If you are very unlucky and do meet another outfit, remember the other driver may not be as new to towing as you.
You'll be fine and it's a great site. Peaceful, great facilities, views and beach.
Have a nice time,
Alex.