A piece of printed circuit board (PCB) with all the components removed if required. (Many such have large unpopulated sections, the ones from my Vauxhall mk3 cav came out of the motorised wing mirrors, which also yielded excellent Buhler motors of the same pattern that Bachmann used in their early Blue Riband releases.). The substrate is thin and strong and the copper tracks enable the wipers to be soldered on easily. I have several locos running with salvaged PCB used for this, also no need to screw attach it, just glue it on.