Dec - Mar are the best months. POST Up to 2 weeks by airmail. There are few post offices. Poste Restante is available with a mail- charge for collection of letters. Most are impassable during the raining season.
Police check points often cause delay.
Temporary driving licences are available from local authorities if you present a valid national driving license. Customs should be respected especially in traditional rural areas. Clothing can be casual and should be appropriate for the hot weather.