Late in the stage, four shielded aircraft will attack. Having the Ion Bomb available here is helpful.
Jedi Heroes also deals substantial damage to ground forces.
The Super Tank (the boss for this level) has a chance to destroy any of the tiles except the four corner tiles and the six at the end of the path. Invest heavily in these.
It destroys tiles in pairs (all tiles other than those mentioned above are joined to exactly one other tile). Keep this in mind when building your defenses -- don't overinvest in any one pair, and don't put two of the same turret on the same pair, or you could lose a substantial portion of that type of defense in a single mortar volley.
After a certain amount of time, the Super Tank will attempt to escape the path. No more enemies will spawn after this is announced, so sell turrets that are out of range and use the energy to upgrade ones closer to the end. The Super Tank is tough -- simply ending with fully upgraded turbolasers on each of the final 6 tiles will not be enough to finish it off.
Investing early in Energy Generators (5 or 6 fully upgraded) will help you afford the expensive upgrades you will need at the end.