I have finished Hark and Ordos missions,i am on atri mission 8 yet and in general i find Hark the most difficult becuase File as you say,they have alot of troops against them. What you have to do is to have a row of 4 rocket turrets,diagonally(like you have but a little more to the south than where you placed them) Have any vehicles and infantry between them and always,i mean always have 2 harvestors. When you have more money,make the rocket turrets into a "step" formation,i.e a rocket turret to the north of where you already have one will be to the west of another one. The entrance to the west should be blocked using walls and dont send vehicles past that point. When you have done that build a light factory and produce trikes. By now your spice feild to the right of your base will be full of enemy harvestors, Via the north route have your trikes haress them and have them retreat if enemy units come. Keep producing trikes and store them to the south of the base,moving them closer and closer to the west entrance. By now almost all your spice south will be finished and so build concrete to the west of the west entrance,then build rocket turrets and move your trikes next to the turrets for protection. Thats it,you should be okay after that