on the subject of USB drive in a car, being a bit of techie I would advise against a portable hardrive unless SSD based due to the fact mechanical HDDs are not really designed for road bumps and being banged about, were as SSD's (still pricey tbh) are not mechanical.. I dont have a large collection of files only about 40gigs for the car anyway, but my advice would be one of sandisks low profile drives.
mymemory stocks these at really good prices and I have used them before and at only 15 for 64gb one wont break the bank

mymemory stocks these at really good prices and I have used them before and at only 15 for 64gb one wont break the bank