For all -- To cut through the noise ... Unless you have a "antique" medium/heavy duty truck that you actually work (even just occasionally -- and going to shows or parades isn't "work" Work is work.) and you have experience with insuring it as such -- you have nothing to add to this conversion, so please don't add to the noise level. Already confusing enough for the OP.
If I can add, we have talked about insurance for the old trucks in
THIS THREAD. You'll need to read all of that one.
The question here (as John stated) is for folks who use their vintage truck(s)
for work ... as
in a business. You probably use a Schedule C to expense the truck.

Please keep the discussion on just that topic.
Thanks,
Peg
