Let me brutally honest about this from our competition experience down at Kennedy in '13. They will not survive past the competition unless your motor enclosures are above excellent. See my link below about this.
https://www.youtube.com/watch?v=DaodHQC_MIo
We had an enclosure that was large enough to allow for some air to move around our rs775s but you will not have that in a lunar/martian environment. In testing, we wrapped our motors in several different materials but even with sand we had thermal issues because heat was being generated quickly in those wrappings. We ended up going with enclosures that had dust barriers around the drive shaft. The encoders we used were also protected with an enclosure that was a bit taller if you look in the video.
We had to replace 3-4 motors out of 6 because this material is so fine that it actually went through two military grade dust barriers and into the motor. I would recommend using CIMS if possible because if any of that dust gets in the rs motor it is done for. We even had melted fans in the motors. If we had the weight we would have went CIM motors for sure.
The challenge is a lot harder than it looks. We qualified in 6th place I think which was the first time UNCC ever qualified.
Also, do not get that stuff on your skin!!!! Clean your rover really well when you come out.