If you really want to go off the grid, Chigaga/Chegaga is a great place to do it. 2 hours by 4x4 from M'Hamid & 3 hours to Foum Zguid. It is rough & it is bumpy for much of the way but the dunes at night sunset/sunrise are incredible. And the stars . . .
It was very lush this year due to rain near the dunes & the nomads have turned their camels loose to graze. Hundreds of them . . . awesome.