As in my candy jar analogy, just because it's there does not make stealing it right. If it ain't for business, then there should be no reimbursement, plain and simple.
From his phrasing, I personally get the hint it ain't for pleasure. You think that they'd just let him out of work for what'll be effectively the whole day? 101 miles one way = 202 miles, or over 4 hours of travel time. Figure 4 hours doing whatever at the destination, there's the whole day gone. Heck, I wouldn't be surprised if he spends 8 or more hours there, in addition to the driving time.
The money not spent at the end of the fiscal year can be rolled over or used on other needed expenses instead of being blown on someone joyriding home on their own personal time.
Obviously you've never studied federal government/military budgeting. Money NOT spent at the end of the fiscal year = money gone, and often money gone from budget permanently(IE They obviously gave you more than you need, so your budget is reduced from then on).
It also indicates, at best, an unfamiliarity with military terminology and working methods. You're the only one suggesting that Leather's travel isn't for work.