When my boat was built the aluminum rod holders didn't have liners in them. It was OK for the Bottom fishing rods because there was a pin at the bottom of the holder. Most bottom rods have the crosshair style bottoms for using fighting belts to keep them from twisting. They are also longer butt sections than down rigging rods. However, with the shorter butts on the downrigger rods the reel seat sat on the aluminum holder and being anal I knew it would wear. I thought about moving the pins higher on some of the holders but ultimately, I found rubber insert caps for my holders on Amazon. They only go in a few inches but keep the seat protected nicely. Long winded explanation of not putting inserts in but a good solution as well....lol