Thommy H:
Completely pointless, since they’ll probably have published rules in a few months, but it was swimming around in my head so here it is anyway. Let’s see how close these will be to the eventual rules!
nitroglysarine:
Why the random movement?
or is it supposed to signify the breaking of the train near battle?
Thommy H:
Steam power: not as reliable as you’d think.
nitroglysarine:
no handbrake? 
only one ‘t’ in benefiting
khedyarl:
I don’t know about that, Thommy. Steam is fairly basic and once you know how to create it, you can harness it relatively reliably. I could see a rule in which if you wanted to push the boilers to the limit, you could move an additional 2d6, perhaps, {in exchange, if you roll doubles, something bad happens}, but just giving it random movement because it’s steam powered seems off.
Thommy H:
I actually misremembered the Random Movement rule for this, because I forgot that you have to move, so I’ll change that. What I might do is have it so you can move 1D6, 2D6 or 3D6 (or not at all), and a double causes something bad to happen. I’ll also link the amount moved to Impact Hits, like the Steam Tank.
Misfires are wrong too - the weapon should only blow up and cause damage if you roll a ‘Destroyed!’ result on the misfire table.
Finally, I need to explain more about the Fighting Platform, as the rules are woefully incomplete.
Thommy H:
Updated the rules in the first post.
Grimstonefire:
There are a few conceptual problems with this, if it is applied to the models we’ve seen. Rather than describe how I’d do it here I’ll make a new thread.
Basically your version relies on the train relies on everything being able to fire in any direction, where imo most of them are going to be intended to be detached.
If however it’s based on a train where this is possible then its looking good. 
Thommy H:
I’ve seen no evidence either way about them being detached. I’ve no idea how you’d even work that in a game of Warhammer. My feeling is that it will be one single vehicle with interchangeable parts. The only pieces we’ve seen on their own are Steam Engines (either with the Skullcracker or the Cannonades), which my rules allow for: the rest of the parts have only been shown attached, as cars.
Grimstonefire:
I’ve presumed that they are dragged into battle, then detached where they need to be. If you had 4 demolition rockets that are not detached the whole train would need to face backwards towards the enemy and would only shoot in a straight line… ;) you’d need to move the whole train to get them to change angle at all.
The magma cannon would be dragged into the heart of battle as well, not the best place for a cannon…
No, they are definitely intended to be detached fluff and rules wise imo.
Thommy H:
Uh…the siege bombard is on a turntable, for a start. I assume the others will be too (the “Demolition Rocket” that’s been shown appears to be just a carriage at the moment…), or it will be easy enough to imagine them being manoeuvred into a position where they can draw line of sight anyway while still being attached. I don’t see how it’s such a huge logic problem, to be honest.
cornixt:
I assumed that they wouldn’t be attached for an actual battle, since the cannonades would face one way and the magma cannon would face in the opposite direction. I didn’t think the skullcracker was related, I’ll have to look closer to see if it has a hitch.
Thommy H:
I’m not sure I understand the point of even making it appear to be a train if it’s not intended to run around as a single vehicle. What’s the advantage to temporarily tethering your war machines together, and why invoke the imagery if the intention is for it to just ferry artillery emplacements onto the battlefield? Surely that just turns it into a support vehicle?
Grimstonefire:
FW do make support vehicles that have little practical use.
Incidently, I’ve been looking around for better shots of the demo rocket, but from what I can see it doesn’t look like it has the same fittings as the bombard for being attached to the train. It does however look quite similar to the magma cannon at the back.
If you look at the pics here the fitting at the back is not going to fit to the train
http://www.chaos-dwarfs.com/forum/showthread.php?tid=8274&pid=141166#pid141166
There is a small grey bit though that I can’t get more pics of, but it looks like it’s in a similar place to the tether point on the magma cannon (which you can see on the far right of the first pic).
So I’m guessing that both of these are actually stand alone war machines that happen to share a fitting to be tethered to the skullcracker for fun.
Edit.
I’ve found a pic with a hook on the back of the main steam train, so it seems both the steam train and the skullcracker could pull the demo rocket or magma cannon
http://i202.photobucket.com/albums/aa117/turelhimvampire/GamesDay%202010/SANY1051.jpg
Thommy H:
So I'm guessing that both of these are actually stand alone war machines that happen to share a fitting to be tethered to the skullcracker for fun.And I'm guessing they're part of the same "Land Train" concept. The truth is that there's no way to actually know until they're released, and then these rules will be a moot point anyway, which is why this is all "for no reason at all". Since we disagree on a pretty fundamental level about what it is we're actually seeing, there's not a huge amount of point debating these unanswerable questions.