The key to this level is capturing the imperial turrets with your Kalaanite troops, which you can recruit when the TRMB reaches a certain point along the valley.
First, though, recruit all of the troopers, then keep your force to the high ground at the edge of the map. Move them to the SE corner, then straight up. Then just click on Brenn then right-click on the TR-MB to put him in it.
"Life. Don't talk to me about life." (Marvin the paranoid android).