As previously mentioned, keep low and rest when the screen turns red. Don't use wooden "things" as cover either... there are plenty of concrete "things" to keep you safe.
Be sure to use flanking maneuvers for the Flak 88s in the trenches. Use your squads as a distraction while you work your way around. Also, use your grenades. They are very effective at killing enemies that are holed-up with an MG-42. I was able to do destroy each 88 by leaving my squads and sneaking around the side. I guess if you need to, bring your bazooka team with you to destroy pesky Germans and the big guns (I didn't need to; destroyed each 88 with a satchel charge).
Overall, not difficult at all.