If its available at the lot your in, I would plug in and then turn on sentry mode. If you dont plug in, dont turn sentry mode, since if you do, as mentioned, you will lose approximately 1 mile an hour, or 24 miles a day. Worrying about charge while you are gone on your trip is not something you want to do, so plug in if available.
If not, as mentioned you would be fine as long as you turn off sentry mode.. I would also recommend turning off cabin overheat protection as well, myself... but I always park in a covered lot when I travel so its not quite as much heat beating down on the car.