VIS optimization on train shaped map

I need some help optimizing a map's VIS to not draw details when not seen, the entire map consists of a moving train which is full of openings.
The walkable parts are only the inside and rooftop of the train, but you can fall out of it so I can't just trim the sky on to it.

I started on making stuff as func_lod and after that func_brush with closer fading but from what I understand, those are more expensive to render and I don't know how to make models :/

The main problem is when walking the hallway, you can see every compartiment in the next car as well, and you can see everything inside the car when on top of the car too.

I have a sample VMF with the main body of the train and some HINT attempts: http://s000.tinyupload.com/index.php?file_id=25715620231675971369

Any help that would prevent unseen details from beeing rendered would be greatly appreciated :}

Isn't this what portals management is for?

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Blame it on Microsoft, God does.

Yes well this isn't a typical map shape, it's relatively easy to manage them in a building and stuff, but for this I really don't know.

Ok I've FINALLY managed to use portals without errors, I had to it enlarge the portal at the door go through the floor, weird...
I made 4 portals per car, 2 on the car-to-car doors and 2 on the windows and side doors (which are never open) and there will be like 10+ cars, are those too many portals ?
Also, I had to add very thin nodraw brushs between the walls of the roof and corners to prevent leaks and portal nightmare due to the curvy edges, but the brushes I added are also in angles and stuff, not great for visleafs, does anyone know a better way to block visleafs through func_details without making their faces invisible ? (which is what nodraw does if I add it as a square block)

But I still got that issue with seeing all details from the corridor, not as severe as before but still significant in certain areas:
[URL=http://imageshack.us/photo/my-images/837/test0009.jpg/][IMG]http://img837.imageshack.us/img837/5360/test0009.th.jpg[/IMG][/URL][URL=http://imageshack.us/photo/my-images/848/test0008.jpg/][IMG]http://img848.imageshack.us/img848/7848/test0008.th.jpg[/IMG][/URL][URL=http://imageshack.us/photo/my-images/40/test0007.jpg/][IMG]http://img40.imageshack.us/img40/3460/test0007.th.jpg[/IMG][/URL][URL=http://imageshack.us/photo/my-images/138/test0006y.jpg/][IMG]http://img138.imageshack.us/img138/4228/test0006y.th.jpg[/IMG][/URL][URL=http://imageshack.us/photo/my-images/687/test0005i.jpg/][IMG]http://img687.imageshack.us/img687/7241/test0005i.th.jpg[/IMG][/URL]

I also have a HINT brush on the entrances of those compartiments which are blocked by 2unit part of a wall, they shouldn't render even from that position :/ I don't know what to use there ... another lower fade portal ? =)