I made an engine cover out of aluminum flashing that I riveted to aluminum bracing.
It rattled and made all sorts of weird noise when the car was at idle.
I went to a thicker aluminum ( about the thickness of a dime ) and that solved the problem, but the thing is surprisingly ....
heavy !
I would suggest using coroplast. There are several members here that have used it successfully.
It weighs much less.
( And one more thing - coroplast doesn't have razor sharp edges either
)