These are simple bits of the creamy yellow insulation foam (left over from Mrs Tom's Toy Soldiers' kitchen extension) carved with a kitchen knife and based on some MDF. I gave them a coat of PVA mixed with some emulsion, a little filler and sieved sand.
The whole lot got a basecoat of Yellow Ochre acrylic paint that I picked up from a craft shop, then drybrushed with some creamy off whites from Wilko tester pots.
They have a pleasingly old school feel to me - reminiscent of terrain I used to see in old WDs. I was aiming for a sort of Monument Valley feel and they'll certainly help block lines of sight for 40K and maybe limit the power of the Eldar Lances.