Well, I don't have anyplace to park my cars except under any awning at the apartment complex that I live at... it's a really upscale place, but still... that doesn't seem to stop the thieves... it actually seems to bring them out in droves... but I'm moving into a house that I just bought and it has a huge 2 and a half car garage, so I'll be parking the cars in there, but my celica and my girl's pink celica.... yeah, I know... will both be parked in there, so our other cars will still be out in the open... which sucks... but there's not shit else I can do except park them in the backyard next to the pool and that's just ghetto.
As for modification insurance, not all companies offer it, but it's an insurance outside of your standard insurance that you can purchase, generally it's like buying a second policy altogether. You have to keep excellent records of all of your installs and all of the purchases though. I even make out receipts for the installation itself even if I do it myself, I have a friend make one out for me, because they will cover the installation itself too. I have USAA, which is military insurance and they are hip to it, so I'm sure that other companies are as well. My girl has I believe State Farm and they gave her a second policy for the same vehicle, so she just pays her insurance twice and that covers her mods and everything because of that.... it just depends on the company... It isn't cheap, but if you have a lot of mods done, then it's worth it...
My Old 2003 Celica was totalled out and I put about $50K into that car above and beyond the $28K that I paid for it.... and I had modification insurance on it and they wrote me a check for $68K, because they figured in about $10K worth of depreciation, so I used that to completely redo a 2003 Celica again, but this time I had lots of money to do it right from the start, so I have virtually everything I can think of done to it right now because I didn't waste money on stuff just to get me by until I could get the better stuff...
So definitely worth it!