Probably way to late for OP. But last year I drove over the marked road on a motorbike. It is extremely secluded and for some parts I met only 2-4 people per hour. There is a bunch of big hydrodams in the middle, so the roads are pretty good. Its also pretty high up (the road runs over and along a mountain ridge), so a little bit cooler. Amazing nature, absolutely no tourists, no humans at all part of the time.
I ended up sleeping one night in the wild (just north of Veal Veaeng). I left the main road and went in 30 meters on an old abandoned logging road. Couldn't be seen from the road (so safe from robbers) and the only sound was the wildlife and a nearby stream. Had I been better prepared I probably would have stayed a few nights on the mountains and done some exploring and trekking.
But pack water and gas, there aren't a lot of stores around if you run out. And do not drive during the rainy season, I did mid may and the roads near Veal Veaeng were almost destroyed already. As far as I know there are no hostels or things until you hit Veal Veaeng (there should be a homestay there), so leave very early in the morning if you don't want to camp or stay in Veal Veaeng.