You shouldnt need to pay to get the mods back!!!, while your car is in a pound awaiting its fate, they you have all legal rights to your car until you hand over you documents/keys etc, things like filters and Alloys etc are easy enough to remove but removal of your heated seats will be a bit more tricky since insurance companies/salvage yards are a bit reluctant for you to do this. Find out from the insurance company first and then decide from there!
If the fate of your car does decide that it is written off, and your allowed to remove the heated seats etc, then I have 1st dibbs on it!
