if its a cc motor i think they are pretty sealed up as it is, maybe a piece of tape over the rear bearing? As for the ESC just blow it out or take it apart when you are done
In motors you want to cover any possible spot sand can get in even extra screw holes. As far as the RX8 goes, Ive got no experience with it. I have run a MM and MMM in the sand with out doing anything to them, I had no problem. I just tried to not let a big pile of sand get in it. It is tough on the fan.