David,
Had the same problem on my '87 westy, local shop was able to do the job
w/out dropping the tank, but they had lifts etc. to work with. At home I'd
definitely drop the tank.
 While there replace ALL the rats nest of hoses AND the grommets that fit
into the top of the tank. In my case one of the plastic fittings that press
into the grommets was broken & was causing the gas fumes at the front of the
van. Shop owner said they get brittle over the years & often break so be
careful w/them. gowesty ( www.gowesty.com ) has a "vanotank" tank reseal kit
for $52.42 that has everything you need to do the job.
Ron Komoroski