The gimbal mounts I have were made locally, so not sure if they are exactly the same as the ones you have. I included a picture of the bases so you can see if they are the same. Mine are just loctited in place... no washers or nuts... have had no problems with loosening.
Second pic is of the bottom end of gimbal mount. Not sure if they come this way from the factory too, but mine have a hole for a padlock. If yours don't I'd add it. Twice I've seen people yanking on the mount and wonder if it would have ended up in the water without the padlock holding it in. More importantly, it keeps them from being stolen. Not a cheap item, these multi rod sets!
Good luck and enjoy. They make it a lot easier when running lines off the planer board or swinging downrigger lines out of the way to create a "netting space" on the transom.

thanks slipnot,
that paddle locks a good idea! the bolts are the same as yours, no washers.

ilucas