You'll find that 99% of kit's and ARF's have their wing joined with Epoxy, why the SIG recommends thin CA I don't understand.
Epoxy is stronger, but most importantly, more flexible and will make the joint stronger.
Use 30-minute epoxy, not the 5-minute version, this gives you plenty of time to adjust the wing and tape it together before the glue cures.

Dry fit all pieces and make a "plan" in your head how you gonna join the wing, practise the steps a few times so you're sure everything fits good before gluing.

I'd recommend you finish both wing halves, then you try fit the wing joiner and slide both halves together, make sure there' s no gaps and everything looks ok.
Then smear epoxy in the holes where the joiner goes in both wing halves, brush generously epoxy on the wing joiner itself and finally join the wing halves to the joiner, making sure it's straight and tight.
Tape together and leave for a few hours to dry.

On more aerobatic, high stress models you can strenghten this joint further by wrapping the center section of the wing with fiberglass and "glass" it with thinned epoxy. Not needed on a trainer though IMHO.


/T5