Hey Munster, welcome to the club! And yet we have another Surdiac owner.
Curiuos to hear about all fellow participants with this stove. Mine is the next step down, (513), and what Fred and the gang are telling you is (of course) spot on. If you keep your hopper full, it'll last longer than if you don't. the heat eats away at the bottom of these things, and not only are they "expensive", they're hard to find. It makes more sense to fill it "after" you scrape the grates cause you'll get more coal in it, but as long as you don't let it get too low, you'll be fine. Check out my thread, (especially if you want a laugh) on "Diary of a Surdiac". People here have been invaluable in helping with my stove. Mine is a love/hate relationship, but hoping to rectumfy it.
P.S.Please learn the picture posting, cause as you know, "everyone loves pictures."