Sarapin pt. 2

I keep getting toasted on Sarapin pt. 2. The farthest I've made it is a 1/4 way up the ramp when I run out of time. I've tried moving artillery into place to blow up the rebel airfield to get rid of the pesky airspeeders, as they are a huge hindrance to the mission. Am I wasting my time? What has anyone else done to make it in time?