Backing plates are a good investment that can save your gunnels from wear and tear which is especially true when your flush mount rod holders are used with downriggers. The heavy load from downriggers and constant tension can begin to loosen screws and wear the opening where the flush mount enter the gunnel. Trolling with big lures and the stress on flush mount rod holders from hooking a big fish can lead to failure when not using backing plates. Play it safe and install backing plates on your flush mount rod holders.
