I installed a Dynon heated pitot on a Gretz mast in the bay with the Stall Warning switch. My install was done after the wings were closed in, so all the work had to be done through the Stall Warning access panel hole.
I cut the Gretz mast hole first on the outside wing skin, then added a 4" wide doubler that goes the entire width between the ribs. The doubler is stepped on one side to sit above the rib flange and is riveted through the existing wingskin/rib holes on one side and has a 90 deg bend on the other side that is riveted through the side of the other rib. There is a slight curve, so you have to do some shrinking on the ends. The doubler is also riveted on the front and aft part to the wing skin between the ribs. The controller box is mounted on the backside of the stall warning access cover plate. That was done so that only two 14ga wires for power had to be run through the wing. I used two 1/4" quick disconnect bulkhead tubing connectors and a mil-circular power connector to retain the removable wing capability.
This is a lot easier to do if the top wing skin is open, but only if you are going EAB on a new build plane. I am surprised that Van's does not offer an optional kit for a heated pitot on the -12iS with the IFR package. The -12 AOA retrofit kit has a lot of the parts needed for the pitot plumbing.
John Salak
RV-12 N896HS