Air Box
On our ZX I find if the boots are in good shape the system lines up fairly well and the clamps hold fine. Maybe a thin film of petroleum jelly on the mating surfaces will get you the slip fit you are desiring?
On a second note: The air box is more than just a silencer. It is a primary factor in the throttle response. Another factor is that the airbox is a tuned chamber that resonates at the RPM of the power peak - about 8000 rpm or 266 Hz. This increases the flow rate about 15% at the power peak - do the math on the horsepower.
After removing the airbox many folks complain of poor throttle response that requires extensive tuning. May not be worth the trade off unless the engine power peak RPM has been significantly changed through other mods (pipe, porting, compression ratio, carb size, etc) that cause the power peak to be higher (or lower) than the factory RPM of about 8000.