I , like many , are begging, please don't start it, or have a friend with fire extinguisher ready to put out the fire.
There is no need to start it until the source of the leak is found.
If the leak is in the area of the gas tank, then your recent seal replacement was not done correctly.

If it's in the engine compartment, number one place to look is behind the right firewall, behind the plastic fitting where the plastic hose joins a short piece of rubber hose that connects to the plastic fitting.

This short piece of hose cannot be seen from above , so it is neglected.
This becomes cracked and leaks onto the hot exhaust, often resulting in fire.
Even if you don't have a leak there you should look at this hose, usually about 4 inches long.
You should replace this if old , and eliminate the plastic fitting completely.

All of us here have heard the reports of many Vanagon fires. If there were more Vanagons in the world, they would surely be the blame for global warming.
They love to burn. We are holding our breath every time you post about your gas leaks.
Please have a competant  mechanic repair your Vanagon and don't start the engine .

Robert
1982 Westfalia

--- On Thu, 12/10/09, Sheilah Rogers <sheilah@SHEILAH.ORG> wrote:

> From: Sheilah Rogers <sheilah@SHEILAH.ORG>
> Subject: Re: PS: leaking gas when engine is on
> To: vanagon@GERRY.VANAGON.COM
> Date: Thursday, December 10, 2009, 3:07 PM
> ps: in case you're curious how it is
> that i could have this same sort of thing happen before and
> yet, i don't know how to get the van out this time, is that
> last time it stopped leaking so i just drove it out. that
> was the one time when the leaking was attributed to having a
> full tank (and brought on a fuel tank reseal).
>
> this is why i don't know what to do with it today. cuz i'm
> assuming it'll still leak...
>
> s.
>