A few years ago, I made this removable rod holder that clamps onto a cleat. Materials were 2x6 lumber, a stainless eye-bolt (opened to hook onto the cleat), flat washers and a wing nut, and some scrap carpet. The plastic rod holder deck mount is installed with stainless screws.
After hooking the cleat with the eye-bolt and tightening down the wing nut, the lumber presses against the gunnel and the deck - rock solid.
It's not pretty, but it's a no-drill, easy to install and remove, non-marring mount.