Ok, so as discussed in the chatroom, but in more detail+solution.
When testing your map i noticed this area was a real pain to traverse, at least, walking past the train carts, from the base. trying to walk around these is a bit of a pain, and escaping past them is suicide. The red circle is a very thin path which needs to be widened. It's too claustrophobic for TF2 gameplay, limiting player movement is generally bad. If the environment is a large cause for your deaths generally players cannot learn how to tackle such a scenario beyond "don't go there". Since it's right outside your base, it's hard to avoid and is something of a trap.
It's mostly a pain to be on either side because these carts reside on a mound which means you have a height disadvantage in an otherwise defencive position. It would probably be nice if you raised the base slightly. 128 units perhaps. So that when you walk out, you walk down a gentle slope.
The flanking of the train carts on both sides, and the stack of wood infront also forces the player to take very linear paths. Forcing a player to take predictable movement is also bad for gameplay. There's no need to remove this piece of cover, but perhaps make it thinner to allow players more space.
If you find yourself in these zones you can kiss your arse goodbye. You also catch the corners (bump into), i'm not sure you can do anything about it, it's just the nature of the model. Red circles represent attackers.
When walking out the base i normally find myself rushing into the middle due to safety, and where i can gain a better view of threats. Also, make the bridge wider, at the moment it's just in the way, and there's no real reason for anyone to "use" it as it traps players and the fences force the player into predictable linear paths which will wind up getting them killed.
I'm not sure how much you're willing to change because you were pretty set with your current layout. But i would recommend moving the buildings over like so to cut the sightline. Then remove that cart which takes up so much space. You can leave the other one in, the issue is less radical here as there is more space around it and it's out of the way. Also, if you move the buildings, it'll have even more space and cut that sightline quite nicely.
This would also be good for optimisation. Even though the train cart blocks direct line of sight for gameplay, it doesn't prevent half the map being rendered from the spawn room.
Potential inside layout. Green is new sightline into base. Those red rectangles are supposed to be stairs if you couldn't tell.