There's a couple of ways to get up there already, although I suppose ladders would add to the look (and there is a ladder entity in gtkradiant, I think I saw it).
Some of the z-fighting doesn't show up when I look at it, but I'll look at it and straighten it out.
As far as the box size, this is a spec from a real one (which I didn't exactly follow):
http://www.transportplanning.com/big1.html
Mine is shorter length, but I like the height. They need to be bigger/smaller?
Oh, and I tried out the gloss/normal map effects added by Torus.... wow! Huge difference, thank you for adding those details (I'll have to remember this for my next map creations)!
Thanks everyone for feedback on the map, I do appreciate it, as I really hope to see the map get enjoyed out there.