I'd be interested in knowing which sheets you have sourced, I've done a bit of a search but can't seem to find anything suitable. Can you post some details. Phil.
Aluminium Lithographic Sheets Scrap (1000 series). We offer all grades of ferrous & nonferrous scrap metal. Buy quality Aluminium Lithographic Sheets Scrap
tekascrapltd.com
They are not very big, but super light I should think a suitable bonding agent & a small over lap they would work well
The benefits of keeping a build light are worth having.
I used 1.5mm white pvc 2400x1200 hygienic Sheets used for commercial kitchens. Bought off ebay 11 years ago now but still as good as the day I stuck it up and completely waterproof.
They still sell it on ebay but the price ofcourse has risen considerably since. Phil.