Open all the windows and doors. Let the air circulate as much as possible.
This stops the formaldehyde gas from collecting, lessening its potency.
Turn the air conditioning on high speed, if it's too hot to keep doors and windows open. Again, this will minimize the concentration of the noxious gas.
Buy six Boston ferns and distribute them throughout the trailer. According to NASA tests, one Boston fern is capable of removing 1,863 micrograms of formaldehyde per hour.
If you cannot afford to buy the plants, you can get them for free from Common Ground Bioremediation.
Heat the trailer to 80 degrees or more when no one is home for several hours. Then open all the doors and windows to thoroughly ventilate the space.
This "baking out" speeds the out-gassing process. Repeat daily for up to a week.
Depending on the weather, air condition when you are home to minimize the out-gassing. It hot areas, just leaving the trailer shut up during the day will likely constitute a baking out.