Finally! I called back Foremost/USAA and scored an insurance policy. It was a two-week battle of phone calls ("We'll have to check with Underwriting on that. Can you hold?"), emailed photos, and explanations ("You say this was a refurbishment project. Who did the electric work?") but at last Vintage Thunder is insured for $10k. That's less than the actual value, but enough that if it is crunched badly on the road, we won't go home empty-pocketed.
For the number lovers, we got $10k collision & comprehensive with a $250 deductible, $2,000 personal effects coverage, towing and $50,000 vacation interruption -- for a total of $266 per year.
One little surprise here is the low cost of towing coverage. I had called Good Sam a week ago to renew our membership. They asked me if I wanted Roadside Assistance for an extra $79. I said, "I'll think about it." Then they offered to transfer me to their partner, GMAC, for an insurance quote. GMAC offered me towing coverage for $6 per year. Hmmmmm.... certainly a better deal than $79, even if they won't come out with a gallon of gas for me.
Unfortunately, they couldn't cover Vintage Thunder under their regular policy because of the "excess value." (They would never pay true value in the case of a claim.) So they offered to transfer me to another department for a "stated value policy." Then they disconnected me. I called Foremost back the next day (who hadn't exactly been great about returning calls either), and got the policy. All in all, not a great showing for the insurance companies ...