I rode the GDMBR with DT Swiss non-tubeless rims, the Stan's tubeless kit, and Continental Race King 2.2 ProTection tires. The weather was extremely hot in Montana, and perhaps I didn't have enough sealant, especially because I was losing some on the rim-tire connection, so I ran out of sealant on one wheel and had to pump up the tire several times a day. Eventually put in a tube until I got a bike shop to add sealant. I had mailed my small bottle of sealant home, which would have solved my problem.
No flats, and I really like the ride (and weight savings.)
Definitely bring a tube and some patches though. I also had the Park Tool TB-2 tubeless tire patch.
The sealant issue is a worry of mine, not sure if I want to carry that AND a tube, or just put in tubes and carry just one tube.
Always have the TB-2 kit... required!