Venting an on-demand water heater?

I'm thinking about installing a water heater like a Triton or Eccotemp L5 on my cargo conversion. I have a tall metal cabinet that could hang on the outside of the trailer, and I would install the heater inside.
My question is, how do you vent one of these? It looks like there isn't anywhere to connect a vent, just an open top on the heater. I would like to keep the battery and electrical equipment inside the cabinet too.
My question is, how do you vent one of these? It looks like there isn't anywhere to connect a vent, just an open top on the heater. I would like to keep the battery and electrical equipment inside the cabinet too.