Not sure how this would relate to your 14 but in my 7, I made a few mounting rails from 3/32 x 3/4 angle that spanned from the firewall to the next aft (middle) former then mounted the VPX upside down. Wherever you mount it, keep in mind that you may need to access it again in the future, after the plane is buttoned up. Install it so it can be acceessed / removed from below.
Carl - - Morrison, CO
flying by: I give up on predicting!
finalizing the wiring - time for smoke test
No smake - Yay!
Sanding fiberglass - Boo!
paid 'til 10-18