So, I'd been thinking of some kind of water-resistant cover. The Rab Survival Zone is a bit OTT so when I saw the Moonlite I thought, "That's the boy for me".*
First impressions: It's light. Very light for what it is and packs up small, much smaller than the SZ. And it's simple, just a drawcord at the top that pulls the "hood" in nice & snug. There's enough room to let my Rab Quantum bag loft fully and it's long enough for me at 6'4".
Moonlite (Top) vs Survival Zone (Bottom)
So, looking good then. All I need to do now is make the time to get some serious Zeds in it.
*Credit to Matt by way of ptc's place for bringing it to my, and others, attention.