Sure, why not, especially when you're living in the warmer south. You'll probably still need to use heaters for most tropical fish, but at least you're electric bill won't be as high as those in the far north
Your garage needs to be fully insulated or your fish will become soup in the summer. A huge tank may be more successful in the garage since temp variation won't be as detrimental day-by-day as it would on a small tank like yours. Even in warm climates, temp variations can be 40 degrees in a 24 hour period. A 26gal would be nothing but trouble in an un-insulated space with no temperature control.