Most likely propane issue is a stove top burner on or the oven, not lit. The other appliances have their propanes outside, so not very detectable by the inside detector. So best place for the inside one is low down near the stove. Exact location not critical.
Some older stoves have tricky oven knob markings that you think you turned it off but it's not. Bad design.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.