Hi. Been looking through the instructions today just to be come somewhat familiar with this kit. There's a full 38 pages worth here!
MadMeex: According to page 36 it appears that the gun unit itself is just pinned into the support arms on the railway cars, and it doesn't say anything about glue being used, so I'm assuming that it can be just pinned 'dry.' I also see that on page 38 it shows how the two rail carriages can be hooked together in their traveling position without the gun unit, so this may be an interesting option to do if a person wishes to make something of a dio. with the gun sitting beside the tracks. It would also cut down on the overall length of this kit too, as I would imagine length-wise, it would give Trumpeter's K-5 a run for it's money all stretched out.
A nice added feature on the instructions on page 17 shows how the tracks sit on the gun unit both in the firing mode and in the traveling mode. The traveling mode shows no sag underneath, but a fair amoung of track sag on top. I figured it would be just the opposite.
There must be some kind of 'support' under there for the track somewhere on the real vehicle. Looks like some research will be in order here.
With the model built in the travel position I wonder if any extra 'weight' will have to be added someplace on the R.R. cars to keep all the wheels sitting on the tracks with the gun unit installed? Of course some added weight could always be added to those tool boxes or inside the bearing unit assemblies beforehand, just as a little insurance.
Good luck and take care, Sgirty