Jens,
I agree. Vapors are a concern.
IMHO, any fumes at all from gasoline are scary. Although, I would prefer to dilute my WVO with RUG because of the convenience (No heat required), but as you mentioned, the vapors would have to be controlled. (I am referring to stationary applications. Vehicle fuel tanks would not be an issue).
Just wondering, people store lawn mowers, weedwackers, Motorcycles, etc in the garage. Most older units have pinhole vents in the gas cap.
A blended fuel might be much more benign and produce much less of a risk.
If a WVO blended fuel stationary engine had a fuel lid with a pinhole vent would that be a problem? Would that not be safer than traditional gasoline appliances.?
Veggie