When we had our pop up, I bought a piece of astroturf from Home Depot. After the first heavy rain it went into the campground dumpster as it retained a ton of moisture. I bought a woven plastic mat from an online pet supply retailer that fit perfectly under my little pop up awning. Once we traded up I went to
www.rvawningmats.com and bought the same mat I have been using since 2007. It still looks great. I will hose it off 2-3 times per season but that's about it for maintenance. No, scratch that - I spilled a can full of bacon grease on it back in 2009. I sprayed Awesome Orange on it, scrubbed it lightly with a brush and it came out looking good as new.
The woven plastic mats are great in that they do not retain moisture, will not mildew, take up very little space, are light weight, are durable as heck and allow sand, water and small stones to filter right through. One of the best accessories ever.