Tri is a good solid item on for gangplank, It just seems the money issue doesnt really give you time to get it along with the other cores in a 3v3, And honestly when i play gangplank i try to be as aggressive as possible, Normally games don't passed the Infinities edge for me, which is why i go straight crit chance, so i can get that as high as possible, as fast as possible.

The squishiness can be a real issue , i agree totally. GA or Warmogs is a must for late game, I mentioned that in the item section ,

Seems decent enough, but i would recommend more survivability over dmg. i also like triforce on him, since his parley hits for like 1.2k wiht triforce and inf edge ONLY. Also, u should get crit dmg if ur gonna get avarice blade build.