I have a main service panel that has two open breaker holes in it. Now I'm adding a sub panel with a RV plug to a 30 amp breaker. The plug receptacle has 3 wires 2 black 1 green. I want hook it to the breaker and ground but the box don't have a neutral bus bar, where do I hook the other wire

Is this 120 or 240 Volts?

I have a main service panel that has two open breaker holes in it. Now I'm adding a sub panel with a RV plug to a 30 amp breaker. The plug receptacle has 3 wires 2 black 1 green. I want hook it to the breaker and ground but the box don't have a neutral bus bar, where do I hook the other wireCan you try to explain this again?
Which box doesn't have a neutral bar? The panel?

Most 30A travel trailer receptacles are 120V/30A.

is this 120 or 240 volts?

120

Don't understand. Are you saying that there is no neutral buss in the main panel?

Or ar you saying you have a main panel with two open breaker spaces and a box with a 30 amp recepitcal and there is no grounding/neutral buss in that box?

Where to hook up the neutral wire and what is connected to
Or ar you saying you have a main panel with two open breaker spaces and a box with a 30 amp
Ive using a 30amp single 110 breaker in one of the open spaces in the main breaker box. The box has a power and ground buzbar,but has no neutral one. If I need to add a neutral buz bar what does it need to be mounted to and how

Still don't understand. Sounds like you have a box with a buss for the hot connections and a buss for the neutral connections. Neutral buss should be isolated from box. Ground connections would be through ground screw in box. Or you could add a grounding buss.

Or you can wire directly to the receptical.

We need a picture of the inside of this panel. Something does not add up.

Also, try to keep things you quote separate. Your posts are very hard to read.