That's what I'd recommend if the Insurer requires individual cataloguing. Photograph each, and keep receipts or ebay email receipts if you have them.
I agree that it would take a long time to do up a detailed (computer) listing of your collection if you don't already have one. I keep a list and photo each new purchase, but that's just for my collection website. But it only goes back about 4 years - the rest is all hand-written, and as much as I've been wanting to transfer it all on computer, it would take aaaaages... and I'm still yet to be motivated enough to do it.