I work for a fire and flood restoration company. We have to clean/eliminate heavy smoke odors from interiors all the time. Anything that can be removed from the smoked area goes into the ozone chamber at our shop. The more porous the material ie. seating, seat covers, fabrics, the better the ozone will work.
All surfaces on the interior should be wiped down and cleaned thoroughly. Then a portable ozone machine should be placed in the trailer for several days. This will eliminate your problem permanently.
A few words of caution. 1.) Do not breath the ozone for any length of time. 2.) It is possible to "over-ozone", the ozone smell will remain for a while if used too long. 3.) Ozone destroys rubber. Any rubber material like door gaskets,
refrigerator seals or even foam rubber pads should be taped off or otherwise protected.
Check your Yellow Pages for local restoration companies, they should be able to help you out.