Rivetted the understructure together. I managed to rivet the rear spear entirely with the use of the pneumatic squeezer. The front spar however was a different story. I tried to shoot and buck the rivets myself but found it very difficult to keep the offset bit stable whilst holding the bucking bar - the result was that I got about 1/3rd of the way throught the first spar and stopped. I was making a mess of too many rivets for my liking - especially in the area of the main spar. I called a good friend and fellow builder (Dawie van Staden) who came to my help and in short order we had both main spars rivtted to the ribs - understructure complete.
NOTE: It's definitely easier to rivet the front spar first as you are able to bend the ribs aside to gain access as needed.
Rear spar rivetted to ribs
Front spar rivetting - spider web like marks in anodising visible