What did you end up doing? I'm looking for a good insurance company, and after reading this thread, I have doubts which one to choose to not face such issues.
Lekta -- Welcome to Stovebolt, by the way!
The first thing you should do is read the Tech Tip on insuring an old truck -- located
here.
And keep in mind a couple of things (reiterating from the Tech Tip):
1. Insurance companies do *not* exist to provide you with good coverage. They exist to make money for their shareholders (which they do by generally providing you more insurance than you need). This is neither good nor bad, just the reality of the market place. Some companies do this better than others.
2. Coverage is something that is unique to *you* We all come to the Insurance companies as unique individuals with unque records/driving experience. No two people are going to get the same quote. So sure, you can ask other people about their experiences but remember this, if nothing else -- at the end of the day, anything said by anyone other than an actual Insurance Agent, authorized to speak for their respective company, means *NOTHING* to you. You MUST get your own quotes and compare them YOURSELF.
3. You can either insure a truck as a collector vehicle (and get comparatively good rates) OR you can insure a work truck. You can not do both (unless you get two policies on the same truck and work with an agent to see how that might work for you). Anything else is gaming the system. Some companies, like Gulfway, will insure a "retired commercial vehicle" at a better rate than a commercial policy, but still not as good as some of the policies you can get for a light truck. They are a little more lenient in what you can do with the vehicle, but there are still restrictions -- DO YOUR HOMEWORK. This is not easy and no one else can do your work for you.
Bottom line: You can use an antique truck for commercial purposes, but you will need to register it and insure it as a commercial vehicle. You CAN register your collector vehicle as such and insure it at reduced rates, but you'll have restrictions that very from company to company. You have to call around and get quotes.
READ THE TECH TIP. Even though I pretty much repeated it here

Stovebolt.com is NOT going to endorse, recommend or encourage anyone to break the law or to deceive an insurance company.
Again, welcome to our site! Tell us about your truck!