Just spam mammoth for avatar. For the devastator, build firehawks. Very useful to shoot them down.
My apologies.
At 1st I also felt Zone Troopers were better than Mammoth Tank in GDI.
After that, Mammoth rocks.
Which is?
I had a few difficulty myself.
Imagine, played the mission 30 minutes...then gave up after they hustle my base
with all those shielded units
I start the mission so many times.
My tips:
Always pay attention (repairing building) while being attack.
1. In each mission, always complete the Bonus Objective (BO) A.S.A.P
In this case, BO is to destroy the Air Node Tower if not mistaken.
2. Speed is the key. Try three(3) refineries, could do better.
Sonic Emitter. AA guns. Mammoth tanks since they can fire ground and air.
3. Sonic Emitter (needs a lot of power plant) so effective against ground units.
4. Rig - deploy near base and will repair units (Mammoth Tank) while defending the
base. Build Sonic Emitter close to it as well.

5. Commando - move it to the right below map (where Air Node Tower is).
When you saw a few building nearby the Air Node Tower , use Ion cannon.
It won't destroy the Air Node Tower building completely. Use the Commando to finish the job.
6. Ion Cannon - disable/'kacau' the invader's Air Node Tower productions (since their units were so menacing...the reason we're having a bad time in this mission.
7. One airfield, more better - the Firehawk is very effective using air to air missiles as well as air to ground bombs.

Once you destroyed the BO, you'll felt a little ease in the game and can start concentrating on
defence of your base.
DON'T FORGET TO SAVE GAME EACH TIME.
Me got till Save Game 50

thanks for the guide.....