Hi Robert
Well well. I'm doing the same tour next month with my mum for 4 weeks.
The roads are no problem at all. Some will have passing places but are good. Do not expect high speeds, more go easy and enjoy the scenery.
Near Thurso is the CC Dunnet Bay site. Superb, by the golden sands beach. Castle of Mey is nearby, well worth a visit plus John O'Groats ( rip of cameraman) and Duncansby Head. Plenty to see and do, even a trip to the Orkneys.
If you happy using your own shower and toilet then CC Grummore on the shores of Loch Naver takes some beating.
Durness for sites is limited to Sango Sands. Stayed there 5 years ago. Pretty good but very windy. We moved further along to teh North West Sutherland coast at Scourie.
The Scourie Caravan site is non bookable, just turn up. Extremely clean and good facilities with a restaurant next to the site. The Scourie hotel and bar is a 5 minute walk away.
You pitch facing the sea. Sunsets are fantastic. Again plenty to see and explore.
If you want to know more let me know .
Cheers
Dustydog