To get back to the OP's original question .........
The method of locating exterior wall studs mentioned by Bluewater will provide you with a reasonably accurate outline of where the aluminum studs are located. A cool, "crisp and dewy" morning is the best time for looking at the walls. Position yourself at the right angle and you should be able to see a fairly distinctive outline of the studs.
As SAD mentioned in a previous post on this same topic, have a helper to use masking tape to mark their locations and make a sketch of your unit with the appropriate measurements.
On the inside, a stud finder might work or you can try applying pressure to the wall or do some tapping with a rubber mallet to try to find the interior, wooden studs.