Well, this level is pretty easy once you choose the right place for the base to get plenty ru's. Go with the main force to the lower left corner of the map by the road to the west and send dire wolves and monster trucks to the center oil rig to kill the enemy tankers. Build up the clan hall in between the three oil patches and the power plant near the south-eastern lower patch. Send the derrick you have and all tankers there. Don't build the power plant too close or you can get these tankers stalled. Upgrade the clan hall to get grapeshot towers and build two of them to protect your rig from the attacks from the north.
Build another derrick and another power plant to the north and send the derrick to the south-western oil patch. Transfer one tanker there. Upgrade the beast enclosure to get giant beetles and build them as many as possible together with shotgunners and use this force to defend. Build one grapeshot tower to protect the nothern power plant. Start creating a decisive invasion force. This should have 20-25 beetles and about 50 shotgunners. Then, go get the symmetrics with all this force. You can enter their base from south-west or south-east, makes little difference. Once you get past the missile towers, krush the power plants, outpost and machine shop and only then, all the surrounding towers.