Any harmful gas sensor recommendation?

I’m making a very huge plan — living in a RV in Palo Alto!
One of the questions is, I need to monitor the harmful gas inside the cabin. This includes CO2, coming from ethanol fireplace, or C3H8(???), coming from propane, or even PM2.5.

Do you guys has any recommendation about sensor of other gas, or any other kind of harmful gas I should be aware of?

Thanks.