I got rid of the formaldehyde smell the old fashioned way from my 2006 Forest River FEMA TT....I gutted it! Actually the formaldehyde smell was long gone. Instead I had to get rid of the musty closed up setting in a storage field smell for a year or two before me buying it smell. It's taken almost 2 years but I'm just about ready to start building a custom interior. Yeah, I'm a little slow on the rebuild. What can I say, life interrupts.
Really though, many people blame the travel trailer manufacturers for the formaldehyde smell when really they can only install what their supplier provides to them. With everything on JIT (Just In Time) deliverys to eliminate warehouse costs, everything is coming from manufacturers with zero time to vent and air out. The TT manufacturers hear the complaints and have to either find sources that do not use formaldehyde, or allow the boards used to air out, both methods add cost to production. I believe the charcoal method is good advice. Charcoal is an absorber of contaminants. Leaving charcoal in the TT (don't get the match lite type) will absorb the oders and help prevent health issues until the full out gassing is complete. Think about it, that's why air filters have charcoal embedded in them. Add charcoal filter pads to your air intake of your AC and heating and you'll be surprised at the difference in how your TT smells in a very short time. Venting the day before a trip and using the filters should take care of any issues.