Definitely going with a backing. When I was going over the boat with the guy that sets them up at the dealer I was looking under and tapping on the gunnels, he says you don’t have to worry about those gunnels we never put backing on our downriggers we just bolt them up. I told him, I will be !! Good example of why I do things myself. I have a good amount of my 1/2” HDPE board left over and I plan on running a full width strip of it under the gunnels it will be long enough to cover 2 flush mount Scotty holders, 1 in front and 1 behind the riggers and back the rigger bolts of course. Being built out of 1/2” HDPE it will be there for 1000 plus years and never rot. Will also be putting self locking nuts and 1” diameter washers, overkill yes but once in I’ll never have to think about them again. Also made my wire harnesses with 10 gauge wire using 30 amp fuse holders and fuses.