If you sleep on an electric blanket and you wet the bed, would you electrocute yourself?
1st of all don't be concerned if you have CO2 in your apt. Its actually CO that you need to worry about. That is Carbon Monoxide. NOT Carbon Dioxide. Anyway, your symptoms are common with symptoms of CO poisoning. I would definitely get a CO detector and put it in your bed room or wherever you sleep. The only difference between the boiler and forced air is that with forced air you are filtering your air whenever the unit runs. With a boiler you have no means of filtering air to catch dust in the air. That being said, a forced air unit never catches all of the dust in your home so no matter what system you have you will always be breathing in dust. I would not blame these symptoms on your heating system unless there is a CO problem in the apartment.
Anything else other than a window unit would be more expensive than the window unit. You could put a roof over the whole trailer. That would cool it some. It is possible to do this with a reflective tarp, but the wind would eventually tear it up.
