Thats defacto gun registration- and worse: registration with a private entity not beholden to due process. Given current realities, anybody who registers their firearm in such a manner can expect a no-knock raid because they were nearby when somebody phoned in an engine backfire as a gunshot.
ATF is not allowed to digitize any of its records around gun sales or transfer of ownership.
So make it allowed that the insurance is tied to the gun. You buy a lifetime policy for that serial number, provide payment, and you're done. Payment can be provided anonymously at a window in cash, if that's your thing.
If you want discounts because you live in a low-crime area, have a gun safe, have many guns, etc. then obviously the storage location for the weapon needs to be declared to the insurance company.