Carbon Monoxide (CO) is an insidious problem. It results from combustion of fuel with oxygen, such as gasoline, natural gas, propane, and even camp fires. CO is an odorless, colorless gas, undetectable by an unaided human. At high concentration, IT WILL KILL YOU. At lower concentrations, it merely makes you stupid, which is a problem because you don't realize what is happening, and are not very capable of taking care of it. With long exposures the "stupid" is permanent. In California, it is required by law to have a CO detector in your house. Sources of CO in a small trailer could be from a malfunctioning propane heater or other propane accessory, or even from the exhaust from your neighboring big rig's generator. CO is heavier than air so it tends to collect in low places or enclosed areas. If it obtains any concentration inside the trailer, you could have a big problem.
If Camp-Inn is no longer supplying a CO detector, I will personally install a battery operated one in my trailer when I get it. Battery powered detectors are commonly available for $20-$30.
One other thing to be aware of is a CO detector has a limited lifetime due to the materials used in the detector, about five to seven years. If yours is older than this it is due for replacement.
I am sorry to put the scare in everyone, but we have only one life!
P.S. A CO detector will not see leaking propane if it is not burning. Of course if it is, you have a much bigger problem!