A good cleaning will probably do the job. You will have to replace all the soft goods in the trailer but new curtains and cushions are nice
We had a 72 that the PO's had smoked heavily in. It took three days to clean the trailer and over a month to get the soft goods replaced. After that, you couldn't tell the trailer had ever been smoked in.
TIP: yellowed light lenses can be soaked in a chlorine bleach solution for 24 hours to return them to a nice white look. This can sometimes cause the plastic to get brittle and break. I thinks it's worth the risk.
FYI - the last trailer we got had not been smoked in but the PO had let some fish spoil in the fridge. Even that nasty smell cleaned up!