I posted these in the joystick top mounting guide thread, but I wanted to make sure to get some help/answers.  I thought of a few more questions here as well.
Here are the recesses for two of my joysticks... 

Here is a closeup of a joystick mounting plate sitting in the recess.  I don't know if you can tell from the pic, but it is perfectly flush with the top of the CP.  I gave myself a little wiggle room with the width and the length of the mounting plate.
What is best to fill in those small gaps between the edge of a mounting plate and the edge of the recess?  Wood filler?  Bondo?  What would you use?

Should I prime the top of the CP before I stick the art to the wood?  My CP is sitting on top of a box made of wood to house the wiring/controls.  What are the best hinges to attach the CP to the box?