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To completely purge moisture from instruments we used to heat in an industrial oven at around 50 degrees C for around 3~ 4 hours (depending upon the size & type) and purge/evacuate cycle with dry nitrogen during this process.
We would then open the door, solder seal the purge tube and ice test on the glass with cube of ice, gently rubbing it around the glass rim (bezel) and working to the centre of the glass. Any internal moisture would thus form on the inner of the glass.
We did have a mass spectrometer for leak testing (with dry nitrogen and helium back fill gas) but it was broken, had been for years and the Airforce was too short armed to buy another for this purpose.
Rubbing ice on a hot glass surface used to result in many glass breakages..if you followed the "rubbing it around the bezel 1st" then you would reduce this cold shock and breakage problem. But it did occur..too often.
This "purge" system worked a treat and you could really see the moisture formation, rapidly! It was fascinating to see instruments fail, then after more purging and baking..Pass! This system worked!
But from this you can guess that many hrs of heating and purging is really the only way to go to completely purge an instrument (camera).
A short purge probably doesn't cut it. But obviously owners do not have small industrial ovens and dry nitrogen HP bottles lying around.
I did develop and trial a method of heating nitrogen and passing it thru the instrument..but alas..fail..you need a very large flow rate of gas! The instruments act as a heat sink.
So really not much to suggest apart from variations of placing it in a bag with inert gas to soak purge! I also suggest that some cameras may not be perfect hermetic seals which is exacerbating the moisture issue.
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