Well I'm glad you had a good time at the show.  Personally I found it to be
a really fun weekend, but traffic on the way in could have been improved.
Anyways, speaking from recent experience I'd say that your vanagon should
be at LEAST 200 miles to the tank full, and probably quite a bit more.

 As for the guage, I experience pretty big variations at low fuel levels
when I'm going uphill and downhill, but when the tank is full it will
always shows full.  Is it possible somehow you didn't have the nossle
inserted properly, so it wasn't puming properly?  I'm sorry but other than
this I'd suggest you should get serious about trouble shooting everything.
If your lucky it could just be the guage itself.  In that case you can
leave it if you want to, just keep track of those miles like you were
doing.

Also I'd definately keep an eye on the oil level.  Just keep in mind that
when the engine is hot that your dipstick reading will not be 100%
accurate, but will still give you a rough idea.  The best is to fill it up
when it's more on the cool side.  This sounds like some funny symptoms,
however, and I'd be careful driving until you diagnose everything.  Just
make sure there's always some good lube juice in there because a dry motor
will self-destruct is a short period of time.

Good luck,
Shawn.