Put it standing upright behind the passenger's seat, and tie it to the
the headrest of the passenger seat so that it can't fall over. Worked
like a charm with mine.
(Or replace the gaskets of the filler cap and of the air vent in the
filler cap.)

On Jul 19, 4:35 am, richard wrote:
My wife and I will be traveling to various harbors in Maine by car
this weekend with our inflatable dingy (deflated) and an old 2-horse
power outboard engine. We will arrive somewhere, inflate the boat and
spend a few hours cruising. It is a great way for us to see some
beautiful places in a very short amount of time. The outboard is so
old that it must be kept straight up or it tends to leak. My question
is: any ideas on how to travel by car with an old outboard engine? In
the past the car has smelled of gas.