So, I just spent about 2-3 hours assembling the packRat on the Mun. I wanted to do one of those 'go to location x, y and z and do experiment alpha' contracts - and what better way than to use a rover. So I pack my pack rat into KAS containers (octocore universal storage) and land on the Mun. However, when I try to assemble the rover, things started exploding. Specifically, whenever I dropped the front, rear or any chassis part they would fall to the ground, stay there fore about a second only to spontaneously disassemble. Wheels worked fine, solar panels worked fine, even the Universal Store KAS containers were glad to lie on the Munar surface for hours (well, not that I tested it for so long, but I imagine they would have). Bringing up the log, I noticed something interesting: It wasn't crash damage that caused a runaway exothermic reaction, but for some reason the parts clipped through the surface, got recognized as "inside the Mun" and promptly executed for breaking physics. Don't know if this is a problem with the parts, KAS or the stock engine, just wanted to let you know. To my untrained eye it almost seems as if the collision mesh (or whatever passes for that in KSP) is buggy somehow. For all those that encounter a similar problem: The way I finally got it to work was by hacking gravity and EVA-propellant and then scramble to assemble the front, front chassis and front wheels while the thing was still in the 'air'. The problem is that the gravity hack appears to only work for the active vessel/Kerbal, as the dropped parts would still fall down, even when I gave them a small upwards momentum before releasing. Another trick that might work is using multiple Kerbals.