Take a look at pages 29iS/U-10 and 11 from the RV-12iS fuselage plans. They show how and where the egress handle attaches to the upper forward fuselage skin. It isn’t complicated, but you’ll have to be very careful to correctly position the ribs that support the handle. The iS skin has prepunched holes, making this easy, but those holes don’t exist in the first generation RV-12 skin.
RV-9A Project: Sold
VAF donation made for 2018