-Well, there are a few tricks.
BEFORE YOU START THE MISSION MAKE SURE YOU HAVE THENS AND THOUSANDS OF CREDITS, THIS MAKE THINGS MUCH MUCH EASIER.
1) DO NOT FIGHT THE WILD RANCOR. You cannot win.
2) Either break the walls to get in, or use the back trail. Destroy the power generator first. That would let you ignore the turrets. Feel free to build pads and swap them around, then swap it for becta/repair pads if needed beyond the front line. Conserve your good units, and heal the meatbags (read grunts) after each rush around a becta.
DO NOT RUSH THE WITCHES ON FOOT, MOUNT THEM ON WILD RANCORS
3) Bribe. Yes, bribe the big weapons. There are a few parked at the east of the first base. And I think they are not moving. So Bribe. Wait until the gauge fills up, and Bribe again. There is a transport in the form of juggernaut. Get the tank too, and the SPMAT really helps. Try to capture more SPMAT and ATAT when you come across them, they are useful, and invincable if you have build pad support.
4) Once you get your First Life ATAT, things will be easier. So stay and wait until bribr gauge fills up before inching on. Use cloak to scout ahead. Rancors are great meatshield, make them by taking your safely guarded witches on foot to the wild rancors, healing them outside battle is a good idea.
I think you can get around 4 ATAT and 3 SPMAT if you take things slowly. Pull the unit close away from the next wave before bribe, so you don't get hit when you try to turn that ATAT around and things.
5) Shiri's rancor is a nice unit, you can always resummon, so use it as bait and suicide rush.
5) On the final barricade with the Moff, I use an ATAT for suppport and blast those towers down with Rancor rush supported by SPMAT, That would destroy the towers. And oh, redguards got pwnd by SMPAT anwyays. Don't worry about losing troops, since they cannot be kept anyways.
Just make sure you get shiri to the moff after everything is sacked.