This was a good move for thompson. It was to maximize the amount of Juneau per diem he will be able to pocket as free money. If he used his Juneau per diem money for a rental car expense, then he would have given up a large part of his daily per diem (a rental car is more expensive than his $800 ride). A rental car expense is a legitimate use of Juneau per diem. But since he won't use per diem for a rental car, there is much more free money he gets to keep.