Depends on how much security the storage facility has of course and whether or not there is electric available.
If you have electric, run the AC set at 85°.
Then, open all the ceiling vents (unless you have the AC running). Cover the tires that get sun. Keep the shades closed. My rig came with front windshield sun screens...if you have those, put them up.
As far as the engine and drive train, not much to do except be sure your fluids are topped.
Last but not least, if it's going to be there for awhile, and you don't have electric, then disconnect the ground cables to the battery sets.