Other threads have talked about some of the issues with useing metal, like delamination issues if it's not on both sides of the core, hard to work with, expense, etc.
As for treating it so it glues well "Lennart" mentioned etching with phosphoric acid, though he may have been talking about something more complicated. I don't know if just a rough sanding would work, maybe.
Stainless is hard to work with. I have limited metal working experience, but the scariest thing I've done is trying to drill a hole in a stainless tube. Way scarier than MIG welding bikes together that kept catching on fire. Now the tube had a 1/4" [~7mm] thick wall and I was trying to drill a 2" hole, but seeing a 2000lb Bridgeport milling machine shake like it's unhappy is just plain scary. Ok, now I'm rambling.
Unless you can find someone with a waterjet or a laser I think cutting an accurate topsheet out of stainless would be very difficult. If you do what the K's have been doing and glue a topsheet on that's too large and trim it down, I think using a router would be deadly. Maybe some kind of grinding bit on a router would be ok.
All that being said, go for it. And take some pictures.
[You know, I think I've noticed that all you guys in the Rockies and west haven't been posting. You're skiing aren't you!
Damn new england. Why did I move here...]
All this talk of metals has lead me to write a sig. Does it show up? Yes.
