Calling all armchair generals! Boudica's Last Stand.

[Renatus]

How I see the defile is like a tongue in a mouth. The mouth being the surrounding hillside /valley covered in trees, and the tongue as a narrow spit of land at the head of the valley.

You say elsewhere that you cannot comment upon the Latin words or their translation but that is precisely the point.  'Defile' is simply the translators' choice of word.  The Latin reads 'artis faucibus' which can indeed be translated as 'in a narrow defile'.  However, 'fauces' has a number of meanings.  Literally, it means 'throat, pharynx, gullet' but when applied to places it means 'a narrow way, defile, pass'.  In a maritime context, it means a 'strait or sound'.  In relation to the battle, I would be looking for a narrow, steep-sided valley which would allow Suetonius space to draw up his troops but which would prevent the enemy from outflanking him and force them to engage him on his own frontage.

I don't think that there can be any question about Suetonius creating a marching camp.  As you say, it was normal practice.  Finding it is the problem.  Lowland Britain must have been strewn with marching camps dating from the invasion and later but few will have survived two millennia of agriculture.