I'm not sure if this has been discussed before, but i've been playing the beta demo senario for over a month now and except for the first time, I have never lost 'the last defense' playing Germans (vs. the AI).
My simple solution to this is to those nasty Hellcats is simply to leave my Tiger where it is, unbuttoned.
Usually I move my Inf. Sqauds down the center towards the Stone building near the road supported by one Stug.
On the Left I move my Halftraks, the motorized Inf. and one Stug.
When the Hellcats appear, I have one Stug in the centre of the road (near the stone building), my other stug on the left dirt road and my Tiger where it is.
The end result is that that the Tiger kills all three hellcats in quick succession while thier fire is divided between it, my stug in the center and while thier flank is under fire from the stug in the left.
I usually lose only one Stug, sometimes 2, but in the 7-8 times i have used this strat, I have never lost the Tiger.
Once all the hellcats are down, I move all forces up to the bridge (with the Tiger), batter my way through and the AI surrenders.
Not saying that I am a great tactician or anything, It just feels rather strange to win this away.