Ok im a Insurance agent. You need pictures of the stuff on the car,you also need Proof of purchase. They will only be insured if the car gets stolen or broken into.Most insurance companies wont cover motor mods. Steros and amps and wheels can be covered. Body kits such as jdm front can be covered.

1st your car must have full coverage insurance, and then you can add the additional stuff you want insured. Keep in mind the higher you go the more you pay in insurance.
Example: i Have my truck insured, i have full stero and tvs installed. I added 4K in addional coverage. Cost me 30 each month. But its well worth it too me