Les Portes de Desert is conveniently located next to the tarmac road, just outside Merzouga, so you can get there easily by hire car and even by touring car, and at the back you can walk straight into the dunes. The rooms are clean and spacious, showers working (and hot too), plenty of good towels. There is a nice swimming pool, breakfast is great.
Possibilities of camel rides, either you can go to the Obera oasis and stay the night in a nomad tent (depending on the season the bivouac can be noisy and overcrowded), meals , matrasses and blankets are provided, or you can opt for a short tour just to see the sun set. The boys leading the camels are more interested in selling fossils at extortionate prices than in the welfare of their clients - they refused to let us mount the camels for the return trip if we didn't buy first!
But even so: the dunes are beautiful.