That sounds like an exciting trip! Here are some travel tips for your visit to Casablanca, Marrakech, and Merzouga in Morocco.

Best Time to Visit:
The best time to visit these locations in Morocco is during spring (April to June) and fall (September to November). This is when the weather is most pleasant and suitable for sightseeing.

Route and Accessibility:
You can reach Casablanca by flying into Mohammed V International Airport, a major hub with many international connections. From there, the main means of travel is by train or by car. The train from Casablanca to Marrakech is about a 3-hour ride. To reach Merzouga, it's recommended to take a bus or car to Er-Rachidia or Rissani, and then take a taxi or a rented 4x4 for the final stretch.

Accommodation and Booking:
There are numerous accommodation options from traditional Riads to modern hotels. It's best to book in advance especially during the peak tourist seasons. In Merzouga, consider booking a desert camp for a night for a unique experience.

Clothing and Essentials:
Morocco is a predominantly Muslim country, so it's recommended to dress modestly. Loose-fitting, comfortable clothes are ideal. Don't forget to pack sunscreen, shades, a hat, and a good pair of walking shoes. If visiting the desert in Merzouga, bring warm clothing as it can get quite cold at night.

Health and Safety:
Ensure your routine vaccines are up-to-date before travel. Bottled water is recommended over tap water. When exploring, be aware of your surroundings and keep your belongings secure.

Local Etiquette and Respect:
Moroccans are warm and hospitable. It's respectful to greet people with a warm 'Salam'. Avoid showing too much public affection as it's not common in Moroccan culture. Remember to respect the customs especially during the holy month of Ramadan.