I never really understood the need for a cover. Mine is open at both ends and I've had no problems. I go through dusty conditions, no problems. I think there's more worry here than needed?
Could be, but this is actually a dual purpose for me in this case. My Medusa motor has a long shaft and the D8 radio tray comes really close to the motor mount. If I have a spacer it pulls the motor back away more from the radio tray. Otherwise I'll have to dremmel out some of the radio tray.