hey, i am building a Great planes piper cub 40 ARF... There is quite a bit of play in the wing joiner/wing joiner slot, is this ok? or, what should i do?

No, this is not good. You need to build up the area to tighten the joint.

Define "Quite a bit".

Can you wiggle the joiner? If so, how much?

Is the slop from top to bottom, or front to back?

Even though the fit may not be snug, it may still work if the gap isn't too big, in either case, a tiny shim against the lesser side of the pocket will force the joiner towards the Major (Spar) side. That's what's really important.

Is this play in it just enough to get epoxy to fill? If it is not much, I would fill the cavity with epoxy, slide the joiner in and wipe off the excess. If it is too much, do as MNF said and fill it.

Alright, thanks... it was'nt TOO bad, so i filled in the slots with a lot of epoxy, and it worked out fine.