Unfortunately, the heat you need to apply to heat shrink would probably melt the foam underneath. As for Al flashing, that's feasible but I think 1/32" plywood is just as strong and lighter, but I am not sure. Hey wait a minute, I have both, I'll go weight a sample. brb...
Ok, I just weighed equal sized samples, and it looks as if the ply is marginally lighter than the Al, I mean almost no difference. I only had about a 1g sample of ply left over from my latest project though, but it took my scale maybe two seconds to show 1 gram for that as opposed to an instant reading for the Al.
Scientific, I know.