1988 Ford Econoline E150 conversion van - Gas leaking out by gas cap .

I have a 1988 Ford Econoline E150 conversion van that is set up as a mobile
grooming van. I’ve had it for only 7 months, and it’s been in and out of the car
repair shop 5 times since. Problems varing from it stalling out at random times
, and it occasionally draining the battery at random times. These problems
don’t happen every time I drive it. Seems to only happen at random times.
Newest issue has leaking out from where the gas cap is. I first noticed it one
day when I went to get into my car to go to a clients. I could smell the gas.
Noticed it was slowly dripping out gas from where gas cap is. I noticed this
happen about 3 or 4 times since. Then yesterday I drove to a clients house,
and when I arrived there I could smell the gas again very strong.I looked by
where the area is you put gas in, and it was coming out at a pretty steady
rate. Not drop drop but I mean pouring out. I tried to take off the gas cap
maybe it wasn’t tightened all the way. As soon as I went to loosen it to take it
off I could feel the gasoline trying to come out.( pressure ) I’ve told my
mechanic about the time it dripped but he just looked st me like I was crazy. I
hope someone here can shed some light as to what is going on with my van
and possibly how to have it fixed. Thanks in advance!