Starting with pretty much the only good offensive position in all 3 stages, those attacking the first point of the first stage, if stuck outside, can sit up on the cliff covering the defensive exit from the control point room. Similarly, defenders can take the same position and cover the offensive spawn exits.
Almost a bit of an exploit but reachable regardless is a few rocks overlooking the exits to the second stage 1 control point as well as the control point itself.
For stage 2 control point 1, defenders can perch above the right offensive spawn exit and fire down on exiting attackers.
When pushed back to defending control point 2, the rocks above and left of the offensive tunnel exits make an effective vantage point for covering all exits, despite being quite vulnerable.
The tunnel exits alone can be covered more defensibly by sitting on (or at least right on the edge of) a pair of black lights on the veranda area.
And when covering the final point of stage 2, defenders can sit just off the edge of the blue loudspeakers overlooking the control point, giving a great view while remaining well hidden.
Rocket jumpable locations on stage 3 of Dustbowl are few and far between, however a demoman may benefit from sitting on the gutter of the roof above the main offensive spawn exit to cover the exits while remaining out of sight.
One can also perch just off the edge of a pair of black lamps rising from the corner into the canals.
The best position for defending control point 1 of stage 3 however overlooks the first control point and is out of range of enemy fire until they round the corner and become very vulnerable themselves, on the ledge of the roof of the main building.
Really the only point on the way to control point 2 of stage 3 is on a piece of wood jutting out from a building in the canals, though it’s terribly exposed. Probably best for demomen.
