Welcome to Morocco Travel forums.
By the way, regarding June it's not a busy time to book in advance so take it easy and slow to make your plans, so you can have a perfect trip in Morocco.
as you can check the Hotels section of Merzouga with them you might book a night in a Riad and the second night to be in the camp at the desert going by the camels. tripadvisor.com/Hotels-g304017-Merzouga_Mekn…
as you seemed that you are going to use the Bus, you can drive also it's very nice to enjoy the landscapes on the way making stops visiting some breathtaking places which the Bus does not stop by.
for more information you can easily use the forum asking any questions.
Good Luck and have a lovely trip.