They painted up pretty easily...I washed them first and primed them "skeleton bone" from Army Painter. For some of the models I drilled out holes (in feel and on bases) to pin them on, but I got a bit lazy towards the end and just started super gluing them down when the foot had a nice flat area to rest on.
Actually the part that was a bit disappointing is that the bases are very much 'decorative' at a slight concession towards utility. Some of the skull piles are so high that its really tough to get a space marine to have a 'realistic' footing on the base. I'm going to have to get bits out and build the kneeling set of legs to something to fit on one in particular. Its very likely that some demon or xenos could fit much better, so your mileage my vary. They definitely give a "Hand me my bolter-holster, its the one that says bad-motherf**ker on it" vibe, so I think I'll be picking another set up.