the trip will be fun and not hard, now you have phone coverage and Gas station at least every 250 km, and then you can find fuel, food and water! I just did it http://www.youtube.com/watch?v=LeOQ6wYqqRI
not from Gambia but from Sierra Leone.
Juest an advice, prepare a lot of fiches fo Wester Sahara and Marocco, with your name, your data, were do you go and were do you come and the passport number and moto plate...at least you will need 20 of them! if not you will have to fill it on a piece of paper!