1988 Ford van stalls mid-drive and won't start for 15 min

I've got a campervan and I drove it over 1,000 miles without issue, but
recently it's been stalling out on me, and then it won't start. It kind of jossles
and dies like I ran out of gas, but I have plenty. So I pull over without power
steering, and when I try to start it, it turns over just fine but it won't fire. It
also seems to after a few minutes start but sputter really slow and die out
within seconds. I also smell a foul gas when this is happening too.

So after 15 minutes, I turn the key and it will start up normally and drive.
But the last couple of times it seemed to start but I heard a pop, like
something slapping the inside of the hood. Didn't sound to good but it ran
fine after that. So I've had it die 4 times now but it never fails if I wait awhile
it will start back up. I'm not a mechanic and I'm in an area I don't know well,
so it kind of sucks. So I'm looking for any kind of advice on what this could
be, and how much I would expect to pay to have it repaired.