I decided to place the Gretz heated pitot one bay outboard of the last access panel bay. This would allow me to easily reach the pitot tube AN fittings and also mount the controller board in the bay with the access hole.
First found the location for the mounting plate. Not shown is the bracket I made to attach the plate to the rib to the right.
I then transferred the plate to the inside on the skin, marking the hole locations and match drilling. After the match drilling, I used the dremel and file to open up the hole for the mount in the wing skin.