Playing OOP w/99

Opponent here is 60/6.6/2.5. Should I just be calling here pf since I will likely be playing OOP the whole hand? Does anybody play this different after the flop?

Party Poker No-Limit Hold'em, $ BB (9 handed) FTR converter on zerodivide.cx

Hero ($110.25)
CO ($94.45)
Button ($117.45)
SB ($108.60)
BB ($112.35)
UTG ($99.55)
UTG+1 ($116.75)
MP1 ($81.10)
MP2 ($99)

Preflop: Hero is MP3 with 9, 9. SB posts a blind of $0.50.
4 folds, Hero raises to $4, CO calls $4, 3 folds.

Flop: ($9.50) 3, 3, 3 (2 players)
Hero bets $8, CO calls $8.

Turn: ($25.50) T (2 players)
Hero bets $15, CO calls $15.

River: ($55.50) K (2 players)
Hero checks, CO bets $50, Hero folds.

Final Pot: $105.50

Interesting hand.

From my inexperienced 25NL background (so take it fwiw) - I might try a blocking bet on the river. I am however stuck as to an appropriate bet size that straddles the line between value and the appearance of weakness.

I would have pushed harder on the flop but I'm still playin 25 and 50 NL. If he had a higher PP I think he would have re raised preflop and when you bet he probably figured you for AK or similar. Turn I probably would have bet pushed back but I'm sure someone will correct me... (VQC donk)