I looked at the IV/IV-P Handbook but still have some questions-

Does the NACA vent/blower provide good ventilation or would it be wise to build in another source as well?

Does the flapper valve do a good job of sealing the duct in pressurized mode- especially if you change over in flight- or would it be helpful to install a positive valve of some sort?

Thanks very much-  Bill Wade  IV-P