I used Platicard for the top and bottom plate (1mm thick) and some 3.2mmx3.2mm strips for the actual body. I have compared it to an E40k Russ I have and it is a bit wider. The gun is two plastic rods glued together. 2 different Diameters...not sure the exact sizes though, now longer have the bag they came in. I am going to change that though, I was going towards simple gun, but I think with some plastic rod, and strips I can make some fashionable heavy bolters.
I am going to try trim down the thickness of the body of the Sponson a bit, because looking at it more closely I do see it is a bit out of proportion.
I will post up a step by step with Pictures soon as I can, it is a pretty simple DIY, the worst part was taking the knife to the Forgeworld model to get the surface flat and thinking 'ok, mess this up and you’re down a Forgeworld Russ...so don't mess up'
Thanks for the props
And now I understand E&C....fiddly, casting sponsons alone would be a PITA