Ah well I've thrown together a 4.5" 'U' beam and will mold it tonight. I saw the original Necromunda bulkheads because people are still flogging them off
on EBay. They're nicely detailed. My one sided casts will probably be nowhere near that. I'm aiming for a spartan I beam reinforced frame - sort of like the earthquake reinforcing you see slapped on the outside of some existing buildings. I'm not confident I could mold robust enough floor tabs either in Ultracal 30. I can see they're either have to be really thick, or would be prone to breaking. I wonder if you could do some simple locking top edge thing though, just to keep card or plasticard floors in place.
I like your idea of chicken ladder wires because I still have a good roll of your chicken wire left in the garage. I could probably cut a table's worth of necro ladders from that in an evening.
One question I forgot to ask was what are the actual physical dimensions of the Necromunda bulkheads? Inches or mm whatever. I just need to create something close to that myself so if I even get around to actually constructing some full Necro terrain pieces they could mix and match with Aaron's actual Necro terrain.