Hi, I am thinking about buying this case but I am worried about the fact that the air vents are blocked when the lid is closed. 1. Could someone share his own experience about how breathing the vents are when it is opened (comparing to no case)? 2. How easy would it be to regularly take the case off and on? will it leave any adhesive marks? 3. And finally, does the MBPTB needs the air vents exposed when the lid is closed and it sleeps? BTW if thats makes any difference, I have the 15'' one.