Today I tidied up and maked out the NACA vent locations and then drilled 3 rivet holes and made some small aluminium backing stips before mixing up some proseal and gluing the NACA vents into place.
I masked up the area first to reduce the mess which worked quite well, and once the vents were clecoed and clamped I removed the tape.
I then assembled and sanded the air vents to the required shape, one corner of each vent needs to be removed and the bench grinder did a good job of this, I then sealed all the edge gaps with silastic before doing up the screws to let it all set. The vents need to be disassembled again so that the angle bracket can be riveted to the fuselage side skins anyway.