Mallo, I haven't checked but suspect the galvanizing will be nearly "invisible" at
radio frequencies. Conducting high frequency electricity works differently from conducting plain CD, the signal will jump straight though things that you might think are
insulators. Like think layers of galvanizing, or even
paint.
If you don't have copper strap, do you have a roofing supply on the island? Sometimes copper foil is sold in rolls for roof flashing, if they don't have it in stock a hardware supply can order it in.