What exactly are you trying to represent you have. If he calls your 1/2 pot bet on flop he obv thinks hes good. Turn changes nothing so your full pot bet is basically nothing as you dont go from 1/2 pot to full pot after hitting trip 8's so it looks like your trying to just bet him off of the pot. Your river overshove is basically a please fold bet. Sure he has reasons to fold but your bet sizing doesnt really represent anything and screams bluff.

Added to the fact that why would you get into the board when he keeps calling. If he calls the flop, no card comes on the turn or river that really changes anythin unless there was a gutshot or open-ender that hit the river for a straight or top pair. Saying goes "you cant bluff a donk" so when your playin micro stakes if you got nothing and your getting called all the way a river shove usually wont make any difference.