Attic Insulation Shield Question

So I'm installing a stove in a room whose roof has very little space between the rafters and the ceiling joists; out near the wall where the stove is going, there really is no space; it is literally about 12" from the bottom of the ceiling joist to the bottom of the roof sheathing. This creates a problem for the attic insulation shield that came as part of the Lowes stove installation kit. The instructions say that if not enough height exists to install the attic insulation shield, an "enclosure from the attic joist to the ceiling joist will be sufficient." What would you guys recommend? I can frame in the opening and lay in a sheet of thin gauge steel on all four sides; or I could use thin plywood. In either case the insulation is prevented from ever contacting the chimney pipe. Any thoughts or suggestions? I'm a bit disappointed that such a significant part of that kit appears to be an item I can't even use. Which isn't their fault or anything; but just saying; I've been tearing my hair out all day trying to come up with a way to use that supplied insulation shield. The main problem is that it's supposed to go on top of the ceiling joists, and I would have to install it so the flange that holds it is under the joists; which in turn would make it impossible to attach the straps for the ceiling support bracket that actually supports the weight of the chimney. Thanks in advance for any thoughts.
Andrew

Thanks for your thoughts guys. Here is a picture of what the insulation shield looks like. That flange around its base is supposed to go on top of the ceiling joist. My problem is that my attic space is not tall enough to accommodate the part of the shield that resides above the flange. Not even close. The shield is probably 6" too tall for this space. I could cheat it down and install that flange against the bottoms of the joists. But then the component that supports the chimney itself would have nowhere to mount. From the supplied instructions it sounds like, if your attic is like mine, you're supposed to fabricate some kind of enclosure, or chase, for the chimney pipe to pass through. Since all it does is keep insulation away from the chimney, I'm not sure how much it matters what it's made of. But I probably would feel better if it were made of metal. I'm just trying to find out if anyone has done this, and if so, how they chose to do it?

Thanks for the input. You're right, the roof is very shallow---2/12 pitch. I've got the pipe about 28" from the wall. By the time you frame in the opening, you practically already have an enclosed chase for the chimney. I was thinking to just line the framing with some sheet metal like you say. Create an enclosed box from the ceiling up to the roof. I hadn't really thought about condensation. Makes me wonder what would prevent the same thing from happening with the shield supplied with the kit. Because it would have cold air blowing across it, as the air enters the roof soffits and travels up to the ridge vent. Hmmm. Anyway, thanks again.
Andrew

Thanks guys. I appreciate the help. WKPoor, I actually understood what you meant; it just didn't come across in the way I wrote my response. Sorry about that. I see what you are saying about condensation. I created a box out of steel that is screwed to the framing---it kind of has to be; there's nothing else to secure it to. But the bottom at the ceiling should be relatively air tight. Moreso, in fact, than the insulation shield supplied with the ceiling kit. The shield supplied with the kit really does nothing but keep insulation away; it doesn't keep air out, and like Matt said, it provides no structural purpose really. I finished installing the "box" and chimney today; now all that's left is to install the stove pipe. A couple of small challenges remain there. But I really thank you guys for your help. It's been a huge savings to be able to do this job myself.