Thanks folks, the big tank is rather fun. There is a vanguard 6mm ordinatus type tank, basically with the same tracks but with a cab on the front and a selection of massive weapons to stick on the top. I’ve got one of those

Chris, I haven’t really had a proper look at the Oddzial Osmy bits, but what I have seen I think looks rather good. Still have lots to paint though, but I may have to get some self propelled artillery at some point.
The cracked earth is simply a few generous splodges of Martian Ironearth (I always poo-pooed the technical paints, but it is so simple and effective) onto the red painted sand and allowed to dry fully, then a generous sepia wash followed with a dry brush and ta-daaaa!
Thanks for the comments.