ORIGINAL: BMatthews
Even with dual load bearing wing rods I would still use a layer of tape to join the panels. The reason being that it holds the tips from slipping outward and the tape also will form an airseal so the air won't leak from the lower to top side. Letting the air leak like that produces a heap of drag and lost lift.
Yeap, definitely with tape. Even full size planes, for example Pipistrel Sinus with removable wingtips, urge you to tape the gap:
http://www.pipistrel-usa.com/manuals...tips-Sinus.pdf