There was a similar scenario posted on Boardgamegeek, and I've been working on the details for one as well. I actually like the addition of turbolasers in the trench as one of my problems with the other iterations of this scenario I've seen was that the rebel ships in the trench could intentionally choose slow speed maneuvers to force Imperials into base contact and deny them their shots. The turbolasers make it so you don't want to linger in the trench.
Yeah, and it's totally from the movie. There's even a "The guns, they've stopped" kind of mechanic, where the Imperial player can turn off all of the trench guns in order to pursue the Rebels in there without risking friendly fire.
In the movie, there are gun towers right along the upper edge of the trench, which I'd actually forgotten about. It just seemed to make sense for the scenario when I set them up that way.
I didn't see it in the rules, but I also think ships entering the trench should automatically align with it. Otherwise it would be very difficult to actually get ships to stay in the trench once there. Even with the drifting maneuver.
I don't see a reason to do that. I think being misaligned may be a feature, not a bug. The trench is wider than it seems, so you have a little bit of room to maneuver, but you have to get the approach right. From there, you can weave (or drift) if you have to and still reach the target. In the movie, Biggs is doing a lot of weaving in the trench run, which looks a little bit like the series of shallow 3 curves that a bad approach tends to create. I kind of like that aspect of it.
Thematically, I'd give everyone a target lock on the exhaust port for free when they enter the trench, but ships in the trench should probably not be able to take any actions, just as though they were avoiding a collision to represent the tense maneuvering, also mechanically it reduces the chances of a kill against the exhaust port on the first attack. (No focus+target lock). The exhaust port it's self seems easy to destroy in one go with your system, it might be better to use an alternative sort of damage where an attack must roll a certain number of hits. It's not about pounding the exhaust port after all, it's about a precision shot that will actually enter it.
No, I'd rather that the trench run be more dynamic than just "race down there and shoot." There are no special rules regarding target locks in the trench, so the timing and ranging of the final shot (which must be made at range 2-3) means you will probably only get one chance at it, and you'll have to roll perfectly (4 hits), which is tricky since most pilots won't have two actions in order to acquire a target lock and take a Focus token in the same turn. You really only have that one turn to acquire the target lock and make the shot before you have to maneuver out of the way if you don't succeed (since you're heading straight for the edge of the play area).
"Almost there, almost there" sounds like a guy trying to get a target lock on something that's too far away. It seems that he only gets that target "lock" moments before he has to fire and pull up. I think that's pretty much what my scenario produces, without changing the target lock rules.
Completing the mission isn't going to be easy for a single pilot to do. You'll probably need to take a second shot at it, just like in the movie. You'll almost certainly need a second ship in the queue to take a shot. But in this mission, you can probably take those shots in rapid succession, instead of stretched out like we see in the movie. But I think it'll be nail-biter. And if you can get two ships into firing position you deserve to win, because that means you've run the gauntlet of surface turbolasers, enemy fighters and trench guns. Hitting the exhaust port should seem easy by comparison.