If you can get a mechanics starter test lead from a local flaps... unless
you already have one... attach one of the alligator clips to the power lug
on the starter and the other to the ignition connection on the starter
solenoid... when you push the button ( key on out of gear) the power goes
directly from the battery to the starter solenoid ... if it pops right off
...the problem is in the ignition circuit... if not ... gingerly jump out
the two large posts on the solenoid... one is the battery supply lead the
other is the starter winding... if it starts ... the problem is in the
solenoid... if not... get another battery ( borrow buy or beg) and jump the
positive terminal to the battery post on the starter... jump the other post
to a good chassis ground... (not the negative battery post) ... If the
starter pops the engine over.. the problem is in the battery or the battery
cables... if not your starter is the last option.. The vanagon positive
battery cable is 10 feet long and notoriously light weight... the ground
circuit is even worse because it is a cobble of connections... check the
ground strap at the transmission closely... take it off clean the metal
surfaces with emery or some such thing... on my own van I ran a #4 wire from
the trans to the negative post of the battery and a # 2 wire from the
battery to the starter... no more starting  problems for me...