turbulence is not completely random so it may be somewhat predictable in its output of the pressure sensor. and exhibit patterns.

Technically it is not random as there is a mathematical description of it in the Navier-Stokes equations, but since these are unsolvable in all but highly idealized situations, in practice it is a random phenomena.

Also let me mention that there is no perfectly random physical source as they all can be modeled by some sort of mathematical equation, so your target should be to use a source with properties for which it would be very laborious and difficult for someone to create a controlled interference in. Hence the turbulence idea.

Just attach a standing miniature fan next to your box and then place a sensor in front of it to measure its turbulence and feed that as entropy into the system (perhaps even regular pressure/velocity measurements may be suitable if an attacker can't find a way to control these props).

Exactly the setup I was thinking would work.