Not the most productive weekend soo far. I had to continue cleaning ribs for the left fuel tank using sandpaper. The little notches in the ribs drive me crazy.
After a full saturday and another 2 hours on sunday, finally got them ready and fluted. Flanges at 90 degress, check!.

The fluting and perpendicular flanges is really critical on the tank. The skin of the tank is .032 which is quite thick and rigid. It is already difficult to install the ribs even when they are perfectly fluted because it is a real thight fit.

I'm a bit worried what this will become when I have to - additionally - put the sealant on. I read about this on the forums and it seems to be not a problem. Once matchdrilled everything should become easier to install.

In between cleaning ribs, I removed the vynil from the left tank and freed all the holes and sides keeping as much as vynil on as possible. The inside needs to be completly removed.

As I said, the installation of the ribs in the tank is really tough. The best way to do this is with 2 persons (ask me where does slipped cleco-scratches on the skin come from if you try to do it alone)

In a first step, I installed the bottom side of the tank to all the ribs. This is easy and straightforward and you can do this out of the cradle.

Secondly, keep the tank out of the cradle and lay the tank on a flat and protected surface. Push with both hands on the top flange of two ribs and try to bend the skin around the forward leading edge of the ribs. This will require some strength.

A second person should then aim for the top most hole on a rib on the aft end of the tank. In this way, you can stretch out the cleco totally and aim for the aft mosed hole in the rib. The tension will be very high on the first cleco and it won't even be able to keep the two together. But once you have contact, and add a second one in the middle, things start pulling together. 

Once they do pull together, put the tank in the cradle and continue adding cleco's in the other ribs. Same procedure, top cleco first near the aft end of the rib, then some more. The first one is always the most difficult. The rest is easy if you fluted well.

Inside view of the left tank with all ribs in place. On the left side, you see the circular opening bottom side  that allow fuel to flow from one compartment into the next.

I ordered the deluxe fuel caps from Andair and the fuel valve. The ones from the standard kit are so poor quality they don't deserve being installed. The fuel cap of andair additionally has an overpressure protection in the cap and can be locked by key.

Now, I should start doing the same on the right tank... OOOoooh noooooooo ! More ribs to clean.......