The photo on the left shows how all wadded up the flashing will be at the store. The one on the right is after straightening. Please be aware that the base is actually square shaped, I had cut off a 2" strip before taking the picture. A hacksaw makes quick work of removing the tube section, and tin snips disect it. After flattening with rollers and a hammer, I was left with the two pieces below, about 200 square inches.
Let's weight down a difficult car, Walthers' iron slag car, shown below. Not a lot of places to hide weight on this car. (Sure, sure, I could just fill the thimble with lead, but that's kind of cheating. Besides, I may want to run them empty.)
You can try using a small ruler to measure the cavity sizes, but I like to use a set of precision dividers. Much quicker and more accurate. Here I'm measuring the curved center-beam of the car.........
.....and here I'm transferring to the lead.
I scribe the cut lines with a probe, then finish the cut with a knife. You can use about any kind of knife (this is an x-acto #2), just be aware you will go through a fair amount of blades. You will have a raised lip along the cut line, just run the barrel of the knife down the strip to flatten it.
The lead is easy to form, and a drop of gap-filling CA holds it in place.
Stacking pieces under the ends. Just make sure it can't be seen from normal viewing angles.
The flashing I used cost a little under $20, and will do a dozen or more cars, depending on the manufacturer. The State Tool and Die line of cars are all-plastic and come without weights, so I'll not only show how to weight them, but how I customize them. Coming in a future installment. I hope everyone is enjoying my ramblings.