From probably fickle memory (and hazy memory of reading common German rail gun emplacement) the "firing" tracks were laid to fit, in place.
Ideally these would be on a curve--about 1 km long and 350-450km radius so that the piece could be trained in elevation by moving it along the curve--cities not generally needing a lot of train angle to fire upon.
A supply spur line was laid to the general center of the arc. That spur track often having other branches, further back, away from the gun. As an Engineer battalion, with cranes and earth-moving equipment wer wanted. Probably a labor battalion, too, to lay tracks and move ammo.
I've seen documentation suggesting Dora had 1500 personnel around her--seems likely given the needs. And, you'd not want to have people be too close to the concusion of firing (or laagers of ammo). This goes double for the field kitchens sleeping quarters.
Which gets us to the classic diorama issue--how to model something that spans a kilometer or so?
A 5 meter (16.5 foot) diorama is only about a 1/3 of a kilometer to scale. These thing boggle quickly.
Which suggests--as it often does--breaking things up into several smaller dioramas. Say a a group of Feldkuchen set next to a short rake of boxcars. A similar display of mechanics working on a switch engine would be apt--or one of the steam locos this operation would need in spades.