Mike- I just bought some wheel weights from Harbor Freight. Worked like a charm on a light box car that kept derailing. They have an adhesive backing. Just peel and stick.
Tank cars may be a bit of a challenge unless you can pop the tank body open.
Bob
Bob, I have the same thing and yes they work well on box cars and gondolas, just not sure for tank cars. I tried to find a place to put them but never found a place where they could be hid or looked good.