I got some sillicone caulk from the local shop which is paintable and was able to install the gps antenna for good.
A little bed of this product is more than enough to make it squeeze out. The purpose of this is to avoid moisture to enter through the holes when standing in the rain. the bottom already has a rubber cushion so I wonder if it's really required but it won't hurt adding the sillicone barrier.
Also did the final installation of the transponder antenna. it requires some cleaning up after thightening the screws. The stuff oozes out all over the place. It looks white here but becomes transpanent when it dries.
Also installed and thightened the castle nut on the tail wheel. The purpose is to make sure that the wheel can still rotate. It can have some friction as it will still "set" within the first hours but it shouldn't be too thight either. You don't want the tire to be stuck and create chafed spots. Installed the cotter pin.
Next up is the com antenna which I completed as well by didn't take a picture.