It depends on how big the openings are. The attenuation through the opening is a log function of the wavelength/frequency, the length of the channel, and the maximum opening size. IIRC, lightning is around 6 Hz, nuclear tops out around 100 MHz, small part ESD is around 600 MHz. If you can get FM radio reception (~100MHz) inside the hull, without running an entenna outside, it's not really effective shielding.

My.02, which is probably worth about .02, is to shield everything using a combination of shielded cables grounded to shielded enclosures, RF chokes, and fast acting fuses. Stick the backup hardware in ESD bags and put it in a shielded cabinet.