In South Dakota if you are carrying more than I think it's 400# of equipment you are commercial and should have commercial registration. We had a van weighed once as a multiop. As for insurance, if you don't claim carrying business equipment you probably won't be covered if they catch wind of it (if not registered and insured as a commercial vehicle)Good call.
I remember when I switched to Geico (for a short while)...
I was using my daily driver to move gear to a gig.
They specifically stated that if my van had equipment in it,
it was considered a commercial vehicle...
and would not be covered if I was in an accident while hauling gear!