Hooking up a 30 amp load center box in an enclosed trailer. Will have a marinco 30 amp plug on the outside . Looking for a wiring diagram that will help me out. Thanks.

What are you looking for exactly? There are no stock wiring diagrams for things like this like there would be a for car or something.
This would get wired like any other sub-panel, only the feed will come from the travel trailer plug.

Will this be a 120V only setup? I assume so since it is 30A. That affects how the panel is wired.