No you don't need to tell them, but just remember you have a cap on your contents how you use it it is up to you. If you have thousands of $ in firearms and related you should have a rider on your policy to cover the extra also up to date pictures and serial #'s are nice.I asked my insurers if they would cover the firearms if they were stolen or the house burned and they had no problem with them and told me they would be covered.
I would rather be sure than find out after something happens. Insurance companies can and will try and screw you over at every opportunity when it comes to making a claim.
There is no need to inform them.