To give credit where credit is due, Martin originally included the small stainless steel tubing in his Insulated Type 27 kit.
To cut this tubing I have a created a fixture while I cut it with a Dremel and cutting wheel. I cobble up some hefty Evergreen strip glued to a small sheet of styrene and drill multiple holes just large enough to grip the tubing and just deep enough to leave a nice length for the sleeve. One hand holds the motor tool and one hand hold and pushed the tubing into the receiving hole. Lacking three hands, I use a vice to hold the fixture. EYE PROTECTION mandatory here.
Inevitably cutting the tubing leaves some roughness which is easy to clean up with a small file and my smallest reamer. For some reason in my experience the clean up is usually necessary on the tubing end and not on the remaining sleeve end which is helpful as one can use the tubing as a handle. Cleaning up the sleeve is trickier as it is so small.
I use ACC to secure the brass rod to be joined, roughing up the ends of the wire on the theory it will give the ACC something to grip into.
I have found it much easier if I build a tank car as a series of sub-assemblies. I think this makes detailing much easier, especially the underframe. To make this easier, I use long screws that not only serve to secure the trucks but also join the underframe and tank. This means I can constantly join and disconnect the tank and underframe as I am measuring, fitting, detailing and painting. Ultimately the tank and underframe will be glued and screwed together.
I treat the handrailing as a subassembly too. With the Precision Scale stanchions secured on the tank I form the two end sections and dry fit these in place. I then cut brass wire the approximate length and rough up one end of each section and secure a section of tubing or sleeve to the roughed up end, leaving of course enough of the sleeve open to receive another section of wire. I then run these through the stanchions on each side. I then fiddle and trim with one of the end railings so that it joins well with one of the sleeves. Then I turn the model around and work on the opposite end and side doing the same fiddling and measuring until I have the second joint.
Then I focus on the end railing to locate where the sleeve will go on these and then secure the sleeves on each end section. Then do the more fiddling and measuring of the side rails until I have a good fit. In the end I will have four sections of railing with four sleeves which I an put in place or take apart as needed.
Why do all of this. One is I like to be able to etch the railings for painting by media blasting it. Also, if the tank itself is not black, I can paint the railings and tank separately. There are things like dome platform running boards that are vulnerable and I like to put these kinds of parts on at the very end of the project and I find this easier to do without the handrails in the way. Also in some cases the ladders have to go on at the same time as the handrails and these are often really fragile and vulnerable and again I like leaving this installation to as late as possible.
Lastly I would add IMO tank cars especially, are more easily built in twos or pairs. There are a lot of steps and I have found it is easy to everything multiple times while it is right in front of me, or as Dr. Frank Peacock, DDS says: "Like things at like times."
Of course, I could be accused of excessive fiddling!