I riveted the lower and upper skins together. I then used a foam water pipe insulator 'tube' to spread the two skins apart to make access to the interior easier. As the top skin is more rigid than the lower I decided to rivet the inner ribs to the top skin first. This seemed to work well so far.
The foam 'tube' used to spread the flap skins to make access easier
Two skin halves have been riveted together
The top skin after finished riveting the inner ribs
