I added 20,000 in insurance for mods to my insurance (progressive)

a majority require you add them to your policy if you want them covered.

You should just do a custom vehicle apprasial. An appraiser will come and sit down and go over all the mods on your car and you can show him copies of reciepts as well. He will give you a write up which you can then turn into your insurance company as well.

My policy with progressive has always automatically covered $1500 in "aftermarket" parts for me. Meaning that they will cover the first $1500 of any damage to non OEM parts. They always make it a PITA to get the money from them, so be sure to keep receipts.