We spend a TON of time in the Moab, UT desert, also camped on Pismo Beach in California for a week. Sand in the slide mechanism has never been a concern or issue for us. Now, all the sand me and my kids drag inside the camper, that's a different issue
I would't worry about it. Have fun and once your back maybe give it a little spray down with water and hit it with some dry (slide) lube.
BTW, we have a 240BHSL.