You want to make an upgraded barracks, about 12 infantry at least 8 rocket troopers, two refineries, a turret, heavy factory, repair pad, 4 more tanks two more harvesters then continue as you wish. Churn out three to four infantry squads with two or more rocket troopers in each squad. Place on the northern rocks. Move the two artillery pieces you get at the start over to meet the incoming infantry in the east but enough south (just beneath the rocks) so they are not in range of the incoming quads trikes and tanks coming from the north and dont kill your own troops with splash damage; use more rocket troopers on the northern rocks with the missile tank behind them to kill the incoming units and an infantry only squad on the southern most rocks to protect the artillery. When the treacherous emperor attacks spot them arriving (having explored the region around the base before with the trike) and use the two tanks to run over the sardaukar then kill any quads then the trikes then tanks from that group. A few rocket trooper backup may help there but only after you squished the sardaukar. It can help to wait until they are attacking a building, like your barracks if you put it above the construction yard. Then move the tanks up north after the enemy heavy tanks are smoke to intercept enemy artillery before they get in range of the rocks and move a squad and quad out to help with enemy missile tanks. Use your missile tank on armor targets as necessary and back up the tanks from range. The hardest bit will be killing the missile tanks which come in last with the biggest punch per shot when you have damaged tanks. Once you have fired on them retreat your quad or the two tanks or your harvester (whatever they are firing at) past the rocks and lure the missile tanks into the base past your troopers with suitable Atreides cunning and the troopers and your own missile tank will make short work of them. Alternatively take the troopers out to the tanks. Key X will scatter a squad so they are not all run over. Get the heavy factory upgraded and build a repair pad before anything else and save the original units and then build more tanks and use the same methods for later waves and with a northern turret you should survive (helps if you remember to repair that). This method works OK for hard so it should work on medium. Placing the refineries helps, one to the south east for a small eastern spice field there and one to the north east beneath the rocks for harvesting the surrounding spice with trooper protection.