Well, if the people who you are talking to have experience with your climate, and growing in it under similar conditions then they may have a better chance to help guide you, I don't know them, for all I know they may have twice the knowledge as me. If you are venting the hot air into the attic then that will be a big help right off of the top, you just need a decent fan to do it with. The AC and the cooler temps are both a plus.
Let us know how it works out, and yes a cool tube should be considered as a back up option.
Adieu