Actually in the -181 its behind the aft bulkhead (accessed via an inspection hatch) but as you say if it dies in flight that's not much use!
Talking about the test itself. What the examiner is after is a demonstration that you are a safe and competant pilot - you don't have to be "ace of the base". If you are at the stage of doing the test then there's nothing in it you don't know how to do. Have a word with your instructor to see if there's anything he/she thinks you should brush up on.
Doubtless you'll get lot of good advice on Pprune but here's something I haven't seen when this has come up before - If your Skills test is in the morning have a decent breakfast or lunch if its in the afternoon - you'll need your blood sugar level good and high!