Once upon a time, someone, Helmet I think, posted a
list of the TUeV accepted wheels for the van (and their
offsets). It should be in the archives somewhere and
should give a better idea of what the german government
believes is safe on a vanagon. Of course, if I remember
correctly, tires cannot stick out from the body/fender lips
in germany, so your offsets might produce only fitments that
will keep the tires entirely in the wheel wells.

dave