Martin, it's been my experience that some non-specialty insurers consider a truck to be a "commercial" vehicle if its anything larger than a pickup, no matter what year it is. Has nothing to do with intended use, titling, registration or any of it. They don't differentiate between current commercial vehicles and older vehicles "retired" from commercial use. If it's larger than a pickup, most of the "car" insurance companies consider it a commercial vehicle and thus either won't insure it at all or will do so at the regular commercial vehicle rate. The agents who are more familiar with the collector vehicle hobby will refer such vehicle owners to the specialty insurers.
Jon -- the specialty insurers who offer lower rates for collector generally don't offer a liability only policy (That I'm aware of). And they stipulate secured storage for the reasons you say and to be able to give us lower rates because we generally drive our collector vehicles less and take care of them, thus we have lower exposure to risk. If you're referring to the main stream insurers, I can't talk to that. I've never had a policy for a collector vehicle that wasn't from one of the specialty insurers as none of them (even my own insurance company I use for my DD's) could ever beat the rates the specialty companies could offer me.
And for collector vehicles, I'm not sure why you would want to go with a liability only policy. For a lot of our trucks, getting suitable replacement parts to repair damage (let alone replace the whole vehicle in a theft situation) is getting to be hard AND expensive. In my own case, my truck's sheet metal is all original and in pristine condition. Finding NOS bed sides, splash panels and running boards is exceptionally difficult these days. I wouldn't dare go liability only. On the newer DD's, I carefully track their value as they age and they do get to a point where a comprehensive policy isn't worthwhile anymore and we switch to a liability only policy. But it's a whole different situation with a collector vehicle, IMHO.
As for Maryland, this state does not require an inspection for either farm-use vehicles or vehicles that qualify for the "Historic Vehicle" registration -- it should, though, as I see a lot of hoopties out there sporting Historic tags... Maryland *does* require (for the Historic tag) that you have a daily driver (regular plate registration). Not sure about the "Street Rod" registration.
Jon makes a good point about umbrella policies. If you have one, you can/should evaluate your policies against your umbrella and the state minimums for liability. Here in MD, it's $100,000/$100,000 as I recall. Most insurance companies will try to talk you into the $300,000/$300,000 coverages and use scare tactics on you to do so. Why pay for more coverage than you actually need? *Especially* if you also have an umbrella policy.
