I don't know how exactly I'd do it, but I always wanted to do a historic operating theatre look on my coven bases. As yet I don't own any coven units, but I always thought of wood or metal looking bases with sawdust scattered across them, splashed with blood.
I like the idea of a bunch of bodies. Like as if the talos' day job is to curate or process the piles of cast-off body parts that accumulate under the coven headquarters, like a sewer system for flesh. You could really go to town on that concept and have pipes sticking out of the pile, or gaps with drains showing. Easy done with vehicle spares, especially any imperial ones.
Should be pretty simple. Just raid your and your mates' bits boxes, paint them quite differently to represent a big range of victims, then add dirt and blood. Gruesome. Might steal.