I use Verlinden-Productions chains. They come in heavy or small. Here are some links..
http://www.verlinden-productions.com/vp_htm_0401_0800/vp0620.htm
http://www.verlinden-productions.com/vp_htm_0401_0800/vp0619.htm
You can also see the heavy tow chain on the rear of my Stug..
http://www.ww2modelmaker.com/modelpages/RRstug3.htm
Hope this helps
Mo/Rob