Do I have to check fluids or do the cleaning?

Apart from specific cases, do not forget to empty the used water, fill up the clean water tank and refill the fuel. 

Give the vehicle back as clean as it was when you first entered it: consider the owner and the next renters! The cleaning steps will also help you ensure that you did not forget anything inside the vehicle (bedding, games and any other personal belongings). If the vehicle is in anyway dirty (outside or inside), the owner can ask for a compensation in order to clean the vehicle, and this will be noted on the rental agreement.