Gas and propane fumes are most likely accumulate in the bilge and cabin floor area.
bilge
Bilge
Bilge
bilge
Bilge
bilge
in the bilge
bilge
They are both heavier than air, and would accumulate in the lower parts of a boat (the bilges).
Without proper ventilation, the fumes are likely to accumulate in the bilges (the lowest part of a boat).
Bilge
In the bilge.