As a Fin Adviser, please DO NOT finance any modifications to your vehicle. If I was a foaming at the mouth old fin adv with a pocket protector, I would be telling you financing a depreciating asset such as a car is a bad investment, but live the dream
The car has some value, even though it will always be in a state of depreciation. Don't do things to this car that will make it deprecate it even quicker, if you don't pay out of pocket.
Last thing you want to do is end up paying for a car + modifications long after the car is gone IE Repo/Loan/Etc..