Derek,
On the subject of an appropriate place of display for a gun, have to say the internal display would be more suitable.
What is forgotten by non gunners, is that the gun is the colours of the Artillery hence, when guns are paraded they are accorded a Royal.
Therefore a gun in a closed well maintained environment is the same as laying up colours in a church.
It saddens gunners to see guns out there, that are not maintained and left to rust away.
Others would not allow that to happen to their colours.