Here are a few models that I created out of bits and pieces, mostly whilst living abroad. Sometimes you can make quite reasonable things out of very limited resources; I think that the barrel for the AT gun in the top left of the picture is from one of the Thunderbird models that you can buy at service stations in Japan. The infantry gun in the top right comes from an Airfix WW1 tank, not sure about the barrel for that one.
Another anti-tank gun sporting a Thunderbird leg barrel.
Last one, actual kitset gun barrels on scratch-built chassis.