Depends on what trades you have ? Are you coming from say a Signals unit or an Infantry Unit. Your trades though due to the fact your not RAC trained/ full crewman (such as Gunnery or Driving) may not count so much.
Again its depending on what you,ve already got and how fast you get the Gunnery/driving trades done and dusted.
No (wait for the slagging), I would be coming from the RLC. Have all my driver quals (less track, and nope i aint a driver or chef) and quite a few instructional quals like MAPRIC, SAA, BTAC, DIT(T) etc but not any Gunnery quals etc.