I love basing models. Not to be over-confident but I think my bases are some of the best I've seen in Epic scale. Of course this came through hours of trial and error but I can give you a lovely demonstration. This may sound odd but hear me out. The sand you want to use is chinchilla sand. You can buy it in any pet store. Now you only want to use 9/10th of it, the other 10th mix fine ballast sand. It is slightly larger but not so large as to draw attention only make the ground even and natural. Next you will need Static Grass 2mm Bulk Unit. Dark Green 1/2 Gallon. Very affordable. Still you will have to trim the grass with a very sharp tiny pare of scissors.
My personal preference is to also put my tanks on bases. When I do this, Land Raiders for example, I also put a bit of green stuff on the base and indent tread marks, let dry and paint them.
As to the base itself I would use GW'd Devlan Mud or Vallejo's Charcoal Brown. I will show you an example if I can find out how to post a photo in this subsection.
http://i64.photobucket.com/albums/h181/ ... aider2.jpghttp://i64.photobucket.com/albums/h181/ ... kaiBT1.jpg