Few years old info as I used to live in LBV.
Gabon is a safe place.
Port Gentil is an airport of entry and a nice little town. Expensive Jet A1 which is funny if you think it is the oil capital of Gabon.
Credit card are kind of useless but in main brand hotel or to withdran cash at ATM (visa only, no master, no amercian X...)
Get some cash, preferably €uro as the exchange rate is fixed (655,957 cfa/€). You would get ripped on the $ change. Other currency are just unknown.
If you have bars on your shoulder, you'll get in and out without trouble.
As there is usually no international flight coming in and out (unless AF already started its "dedicated A320 flightdirect from CDG), the security check are pretty easy going. But bring your yellow fever certificate with you... You don't want to recieve an injection at the airport medical office...
I don't really remenber fences around the airport...
Good sea food, beautifull woman and fair temperature as POG is almost an island.
My 2 cents...