Since the air gets pushed over the evaporator coils to get cooled before entering the trailer, I would get a couple of cans of A/C coil cleaner and use it liberally on all of your coils. Be very careful on these coils and fins as they are made from very thin metal and will very easily distort and negatively effect the efficiency of your unit.
Also, I would clean all of the air passages in and out of the trailer within the A/C and toss the filters and replace them.
Hopefully, all of that tobacco crud will be removed, along with the smell
Let me know if you can't find the coil cleaner.