Something the pros used to say back in 2007 was to never build static D. I think this carries over from the Total Annihilation days because static D in TA was very expensive and low ranged.
In SupCom it was made far more effective and since I have habitually started building static D in my expansions again I have noticed myself winning more often.
So my recommendation is to build static D and let it look after your expansions for you! And before someone says it can be destroyed by a single arty, it takes micro from the enemy to do that which significantly delays him and thus gives you time to respond with your own units.
I used to build static D but spent a long time trying to get out of the habit of it, based on flawed wisdom. Now I am getting back into the habit I find my expansions not falling to a swarm of t1 tanks anymore and it's really cool!