We do all kinds of backing plates
out of cast Almag 35 (aluminum-magnesium). This eliminates corrosion
from the SS nuts/bolts and is much stronger, and often lighter, than many polycarbonates, let alone regular aluminum
. We carry backing plates
from 6"x6" all the way up to 12"x16" all by about 1/2" thick. These get used for mounting cranes and davits
off the transom of powerboats so they are well strong. Send me a private message for more info.
I have worked with StarBoard in the past and find it is much more useful as an engine
room cover, etc. It is easy to work with and does not melt when you cut it.