What you need to do depends on where you fly I guess. If you fly at Lost Hills where your model is cushioned on landing by the dying breaths of unicorns then you don't need much more than the thick ribs. If you fly in places where wild animals literally rip your wing tips off and/or you fly on runways so hard as to defeat the, er, well I digress.
I use a brace from 2mm PCB material (glass fabric) which sits inside the spar flanges. I pack either side of the brace with balsa, sand to size and glue in with epoxy.
The TE I rienforce top and bottom with 2 x 1/2 tows of UD carbon, attached with cyano and sanded down to zero thickness at the ends - total length about 30mm either side of the joint.
The d-box I rienforce with two layers of 50gms glass cloth attached with cyano bit I've seen good results with UD carbon as well.
All these actions result in a very strong and stiff joint able to resist the effects of a rutting Haggis (but then you knew that, didn't you).