Bummer that you didn't get any replies... I was hoping to hear some experienced mastiff people chime in here...
The skin and ear issues may be related to allergies - I have heard (on this forum) that many mastiffs are allergic to chicken, which is any just about every kibble and can of food you can buy.
Our EM puppy had itchy skin and one gunky ear (the other was perfectly clean). She was eating Solid Gold Wolf Pup, which is bison and rice based, so no "known" chicken on the ingredient list. Once we got her on a raw diet things got better, but still the occasional itchy skin... once we got consistent with adding a salmon oil pill every day and stopped chicken all together, the itchies went away. Her "gunky" ear is nearly as clean as the good one now - after 2.5 months on raw. She's just over 8 months old now.
If you're looking for food recommendations, check out posts by Smart_Family. The Wolf Pup isn't on her list, but we did well on it.