The main unit on my 87 is under the aft dinette seat. The control panel is located on the surface below the V berth.
I have two vents. One is up in the V Berth, and the other is up on the left above a shelf as you enter the cabin.
There is no vent in the aft berth, which is kind of stupid. I've thought about trying to run one back there, but it looks like it would be a major project. Getting the vent back there is one problem. You could probably go under the steps, through the bulkhead, and run it around in the engine compartment to a spot where you could tap it in to the aft berth. But, I think it might invlove drilling holes where you might not want to. I'm thinking that might be why Searay didn't run one back there to begin with.
My wife and I sleep in the aft berth all the time. The kids sleep in the V bunk.
I have two small oscillating electric fans that I keep on the boat. I bought them in Wal-mart a couple of years ago. One stays on the shelf up next to the V bunk, and I keep the other on the Dinette table.
I turn the A/C down low before we go to sleep and run the fans. I lock the forward fan facing aft, and lock the one on the dinette table facing down and in to the aft berth.
It sounds more complicated than it is. I've found this method to keep the entire cabin, including the aft berth, nice and cold.
We have central A/C at home and I am addicted to it. My wife often complains that I keep the house too cold. That being said; the way I run the A/C on the boat at night keeps us nice and cold in the aft berth. We sleep back there with a warm blanket even on the hottest nights.
It ain't fancy, but it works, and it's a lot cheaper and easier than trying to run another vent back to the aft berth.