Are you sure thats the best place for them?

I got a stainless arch made on the stern and mounted a big (2m x 1m) panel horizontally on it. It serves as a solar panel and roof for whovers sitting on the poop deck seat if its raining. Horizontal minimises average windage and it doesnt matter which way the boat lies as far as sun on the panel goes.

Objects very close to a radar can desense them I think you'd have to turn the radar on and observe a distant landmark (ie heads maybe) with and without the solar panel to see the effect. If its a radar with a bit of grunt nearby metal objects might scatter the transmitted power onto you on deck and some people are concerned about the health effects of that.