This comes from Electromagnetic Fields and Waves by Lorrain et al, page 77 on a Hollow, ungrounded conductor enclosing a charged body:
The surface charge density at a given point on the outside surface of the conductor is independent of the distribution of Q in the cavity. It is the same as if the conductor were solid and carried a net charge Q.
1) I don't believe this. As I move +Q around the inside of the cavity, this will affect the distribution of $-Q$ on the inside surface, which must also affect $+Q$ on the outside surface to keep $E=0$ inside the cavity conductor.
Inversely, the field inside the cavity is independent of the field outside the conductor. The conductor then acts as an *electrostatic shield.
2) I don't believe this either for similar reasons. The external fields will affect the distribution of $+Q$ on the outer surface, which must affect the distribution of $-Q$ on the inner surface and therefore the electrostatic field inside the cavity, to maintain $E = 0$ inside the conductor.
So am I correct to disbelieve that an ungrounded conductive cavity can provide electrostatic shielding for the reasons 1. and 2. above?