We went through this recently with our 1963
Bambi. Called our regular carrier and told him what we have... My hubby has just completed (98%) restoration. I have a excel spreadsheet where we kept track of our expenses to help establish value. That information coupled with photos (they were willing to come over and take the photos, but we live in a very small town and it is all local folks...) and a sort of average of restored airstreams on ebay and such we came to an agreed value for coverage.
We probably have more $$ into our Bambi than the max insurance, but we aren't too far off. I went for a very low deductible and the yearly cost was very reasonable. Hopefully I will never have to "test" the insurance waters with it!
There are some specialized carriers "out there" that deal only in vintage type vehicles (you can find them at hot rod shows, etc.) and they are used to establishing value. We have had classic cars in the past and coverage was easy ~ however, we were fortunate and never had a claim so I couldn't tell you how good they are
they were willing to take premium payments cheerfully!
At any rate, I would talk to your insurance folks, take them pics and give them a $$ amount you feel would cover your expenses and see what they say! If you aren't happy, go shopping!
Mrs. NorCal Bambi (traveling in S Tardis)