Like most things electronic, there is a simple answer and a complex one. A car is a faraday shield only under some circumstances. Lightning is one of them. But RF is not.

Various type of electromagnetic fields can be blocked by faraday shields, depending on the shield type and the field type.

What type shield works for what type field is a very complex subject. In general, if you put a transceiver in a metal box with no holes larger than about 1/10 wavelength of the field of interest, and ground the box to a suitable ground, the contents will be immune to the exterior field.

In practical terms, it is almost impossible to shield a radio from a large nuclear burst unless you are very far from the burst.

What exactly do you want to do? Nothing you can do within reason will keep ham gear safe near a nuclear blast. There is lots of stuff about this on the web, but mostly it is quite complex.