The 12 volt battery in the HEV is disconnected automatically if it detects a discharge. You then reconnect it with the battery "reset" button on your dash. This works really well! So you can do nothing if you want. There is a way to disconnect the 12 volt battery manually if you want to take the extra step but I don't think it is needed. It is a lithium battery, if it was lead acid, then for sure you would want to disconnect it.
I'm expecting to park my own HEV for 6 months to a year for an overseas trip in November and the only thing I plan to do is pump my tires up like they do when leaving the factory - less chance of a flat spot when I return. Traditionally you put your car up on stands to reduce potential damage to tires. I think the factory uses 70 psi when they ship cars, I'll use whatever the maximum pressure it says on the tire (plus maybe 10%).
