$100 PLO on stars, 5 handed. Opponent has $120, I cover.

I get [Ks][Qc][4c] and limp. Opponent raises from SB. All fold, I call.
Flop (pot=$8): [Kd][2h]. Opponent bets pot, I call.
Turn (pot=$24): . Opponent checks, I bet $15. Opponent calls.
River (pot=$54): . Opponent checks, I bet $30, opponent calls and wins with [Ad][6c][5c].

I felt that my line was representing strength and not a steal, but apparently this was not the case? Suggestions for a more convincing line? I thought that if I'd raise the flop I'd only get action from another K, but maybe I got too greedy...

I don't think it would have mattered much against this dipstick if you raised the flop or not. This is a tough spot because your top trips/top kicker doesn't seem to win these confrontations all too often, so it's hard to say "you have to bet full pot there" because it's just as often that you are behind to a made boat.

I would have repotted the flop to see if he made his boat or not. If he flat calls then you are probably looking at another K that hasn't boated up and can proceed from there. In this case he might have folded (should have, but who knows) on the flop. If he repots then you probably have odds to chase anyway. I can live with getting my stack in here on the flop with this hand 9 times out of 10.