I'll just add that these smoke detectors are generic i.e. made for residential. Our ceilings are WAY lower than in a house henceforth the pain in the butt of them going off all the time.
The propane detector: situated all the way in the back usually in the bedroom is designed to save you when you are sleeping. Ya all my serious propane leaks that almost killed us happened during the day in the front of the MH where all the propane appliances are......and the darn thing never went off. I guess you have to be sleeping in the middle of the night to be saved by 'that' detector. :R
I ended buying a plug in residential multi purpose alarm like I had in my home that detects natural gas, methane, propane, etc. and it's plugged in the FRONT of my MH.