I've found that as I "gather" more stuff I need increasing larger cases. I bought the first GPC case which doesn't offer enough room for the Mavmount especially if you have a bunch of the extras.
What I've done is buy a LowePro backpack that holds all my Mavic gear and then some. Has room for all the additional stuff like Mavmount, a nice slot for my Ipad Air 2 or Ipad Mini 4, Hoodman shades.
When I need the added protection of a hardshell case. I just put what fits in the case to protect it from vibration and hard bumps. Items like my Mavmount I just put in a separate bag and put it in my motorcycles top case...