Normally, for a split turret like the model has, an over-pressure system is usually considered sufficient to protect the fighting compartment if it is exposed when the gun is depressed. It needs to be quite strong though, as I understand it. As has been suggested, isolating the autoloader from the crew is however considered a better idea if possible for NBC defence.
Early oscillating turrets had considerable problems with NBC defence with the quite considerable range of movement. This is what led their major exponents, the French to largely abandon their use after the AMX-13. However, they didn't stop working on them and by the late 1980s they were back on the market in a range of smaller, APC based turrets mounting up to about a 90mm gun. They claimed they had beaten the problem with sealing the turret but I never learnt how. Perhaps again it was use of a large over-pressure? As far as I am aware, no one, not even the French Army bought any though...
The use of a cloth/leather/etc. cover would help considerably. Making it bullet/splinter resistant would help even further. However, until the 1990s, the cost of using synthetics was against widespread use by most military forces. That it was also resistant to stretching would I feel tend to tell against it's use as well.
