"MikeM" wrote in message
...

The reason that I dont have problems with my boat, truck and airplanes is
that they have large, sealed tanks.

Those are all vented, although depending on the year the newer cars vent
into that coffee can looking container under the hood. A small portable
tank is only vented when you open the vent to pour out the gas. Close that
vent and it is airtight.