Very interesting design, curious as to how often do you win defenses?
A couple things for sure to consider - make sure your squad centre is full! That is half the reason behind a good defense. Your Deka is good, great for defense, what level is it at? I leveled mine to 10 at soon as i could. You need a lvl8 HQ for a lvl 11 Deka (upgrading mine to 11 as you read this).
I also see only a few mortars, they are good against rebel infantry and the majority of rebels use lots of heavy's and soldiers (+ those infernal medic droids) The medic droids are also taken out by mortars easier because of their splash damage. The rocket turrets are not as effective against infantry. maybe change some of them?
Lastly I like to use the whole map and spread things around (resource buildings and landing pads) so it forces attacking units to be all over the map and it takes longer for them to get to your buildings. Having them clumped in one large area makes it easier for attacking. Hope this helps.