I haven't done it yet, but there's a couple of things I'd like to try:
1. Exped megamat = really nice and comfy airbeds. Interested to see how it fits in the back of the PS3
2. Occupant locking locks the vehicle, without the alarm being triggered. Occupants can still open the doors from inside. I'm not sure what the difference is from just locking the door from the driver's seat door controls?
3. Scheduled heating/cooling cycles throughout the night - this might also help a little with condensation.
4. Condensation is going to be a challenge. There are some good products on the market for more mainstream vehicles (eg. Landrover Defender) where you can buy vents that fit and prevent mosquitos etc getting in. But for the PS3, I dont think we're going to be that lucky. So maybe one of those over the door-frame nets/sunshades which should allow you to crack the rear windows without getting eaten alive.
5. Window Blinds (including the roof blind!), will be useful if the sun's coming up early. They make it feel a little more cosy and secure too.
6. I'm not sure if/how you can open the boot/trunk from the inside - I assume there's a button but it's not always the case.
7. I'm also interested in the self levelling the car does automatically. It's unclear if it only self levels when driving, and then airs down when parked. It certainly did alot of hissing and moving this morning - so I think it's probably only self-levelling whilst driving..

 

1. Exped megamat = really nice and comfy airbeds. Interested to see how it fits in the back of the PS3

I have a Duo LW+, which is too big.
You should go with the Duo M.