What do you use to attach aluminum to wood?

I'm updating the roof on my foamie hybrid to give it a nice reflective coating. I've already got the frame done and have some 1/8" plywood glued and stapled to the frame (which, unfortunately, added a lot more weight than I was hoping). To get the reflective coating while keeping the weight and cost down, I found some ultra thin .0086" aluminum flashing that I'm planning on using:
http://www.amazon.com/Billy-Penn-Valley ... m+flashing
My two big issues with this are, of course, how to attach it and what I should be doing with the seams. My current plan is:
* put a coating of oil based polyurethane on the wood to help protect it
* bind the aluminum with contact cement and machine screws around the edges
* use some aluminum flashing sealant (basically grey silicone caulk) in a paper thin bead to seal the seams and screw holes.
Would this be a viable solution? Is there a better solution? As a horrible point of hindsight, would you anticipate this to be lighter than having just used some .032" or .040" aluminum sheet without bothering with the wood at all?
http://www.amazon.com/Billy-Penn-Valley ... m+flashing
My two big issues with this are, of course, how to attach it and what I should be doing with the seams. My current plan is:
* put a coating of oil based polyurethane on the wood to help protect it
* bind the aluminum with contact cement and machine screws around the edges
* use some aluminum flashing sealant (basically grey silicone caulk) in a paper thin bead to seal the seams and screw holes.
Would this be a viable solution? Is there a better solution? As a horrible point of hindsight, would you anticipate this to be lighter than having just used some .032" or .040" aluminum sheet without bothering with the wood at all?