Thanks for everyone's advice and insight. I have had long talks with my insurance agent. She initially contacted several insurers such as Hagerty to see if the camper could be brought under their policy on the basis that I wanted: a stated value for the camper based on restoration values. The answer was no. Both to the question of vintage TCs and to the question of stated value.
So, she said she decided to call adjusters in her company and ask them how to solve the problem. The adjuster, she said, directed me to get an appraisal at a reputable company that DOES RV REPAIRS. Not an independent "expert" but a real hands on RV shop that is familiar with the vehicle. I was thrilled by that since the shop they mentioned is where I go for any repairs that I need. Its nearby and very competent: Kampers Supply in Carterville, Illinois.
Secondly, I need to have photos on file with the insurance company and maintain receipts that prove the value of the parts as well as the labor.
This is roughly what everyone has been saying: at this point in history vintage TCs are worth what the adjuster says...and there is not much one can do other than photos and receipts.
One more thing. I have a lot of properties under this insurance company since I do historic preservation on houses that are then placed into the rental market. Its clear to me that was a factor in my insurance company's advice. I think if you are an average guy with homeowners and auto insurance your mileage may vary. I don't think that's right - I think we should have some way of insuring our vintage machines at an assured value regardless of our other business interests - but it looks like that is a key factor.
So far I haven't had any repairs that I would have made an insurance claim about. When I crashed into an overhanging eave and knocked out several aluminum panels, I treated it as a learning experience and we did the work ourselves. But if a storm knocks a tree down on my camper, and its not mounted on the truck, I think I may have to pound sand regardless of the assurances from my insurer. My truck insurance covers my TC.
And that's the way it is.
