If you mean apart from Visas', innoculation shots etc etc of the normal tourist, the rental agency will need to approve and write a authorisation letter allowing you to remove the bike from the county of registration or you will not get it past the border posts unless you revert to the age old african custom of bribery. The agency will also need to provide you with a Carnet du Passage.
Have you spoken to the rental agency? I find it unlikely that they would allow such a trip due to the insurance etc involved. If they are OK with it, please let me know who they are, I would be interested in such a trip......just not on my bike.