I don't know for sure just what smell you are trying to describe.Is it a musty smell, or is it formaldehyde? Musty would more then likely be caused by moisture. Formaldehyde, is used in most of the building components in our trailers. When ours was new it smelled pretty strong of formaldehyde. I pulled it out of the shed and let it sit in the hot sun totally closed up, and like Hunter said, I placed containers with ammonia around inside the trailer and let it set that way for---I don't know whether it was 1 or 2 days. You almost need a gas mask to go in there and retrieve them and get the windows and doors opened up.
but it did the job. I'm lucky in the respect we have a building our rig sets in here at home, and I leave windows and door open "all" the time, year around. I also have a oscillating fan in there that gos 24/7. Keeps air moving and has to help when the humidity gets high.