I use the same holder as Snow Dog. Pics are in my thread on finder and rod holder set up but maybe I'll post here again
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As you can see, I replaced the C mount with the platemount, which I screwed down to the thwart. This is rock solid, doesn't move, is light, strong and small. Not sure why it didn't work for you MT but for me and my buddies its all we'll use.

Moonman.