Propane Detector would be located down low...floor area \ Typically in toe kick area of kitchen cabinets etc.
It alarms when a propane leak occurs as propane is heavier than air and settles at floor
BUT TRAILER BATTERY NEEDS TO BE INSTALLED as it is wired directly to battery and NOT fed from converter.
Something like this.........brown/white/black
And they also have a shelf life of 5-7 yrs. so your 10 yr old one needs replaced
You stated fridge wasn't cold when you noticed the smell and flame was still on.
If it IS a propane leak..........then fridge outside compartment would have been filled with propane vapor and it would most likely have gone boom.
If fridge flame went out...gas valve would have to have stuck open to allow any gas to flow w/o a flame.
Look for any yellow residue in outside compartment around the burner area (main flame is small-------no pilot flame used)
Plugged into electric at house then try running fridge on electric vs propane and see of fridge will cool down.
Smell, no cooling....good chance fridge cooling unit is bad. That means replace cooling unit or replace fridge....neither cheap