I have my insurance with The Rielly Insurance Group for various reasons, which I have previously mentioned in other posts. (The bill comes from Chubb and the check is made out to Chubb.)
www.historicfirearms.com
In essence, it seems like Rielly had a little less red tape, and, more importantly, answered my questions instead of treating me like a 6 year old.
As to Nationwide, you should check their prices and compare them to the others. You will find that the rates are much higher than those of the companies that write specialized insurance.
(I do not know how true the following is but I have heard that a few companies will not insure anyone who has firearms. I do not have any personal experience with this.)
If I had my collection as a rider on my homeowners policy, I would not be able to afford the insurance.