Look around for some bevel siding it's perfect for ripping down to
make the slats with. And if you use cedar and stainless fasteners it
will last a long long time.

Thanks guys, for all the suggestions.
I solved the problem and also made it easier (I think !)
I bought a metal louvred panal at HD for $20.oo
I cut a square hole in the existing arched panel.
Fit flushed from the backside. Should be OK.
If it passes the eagle-eyes of the *Association"
we'll be in business.

Smitty