Hi
A C182 is probably the most ideal to do the whole Namibia experience in. If you have C210 experience try and get one of those. It makes those long trips between destinations so much quicker and much more pleasant.
If you want a C182 then I can recommend a Pieter Hartmann from Eros Airport. He owns and runs the maintenance division called "Aviation Centre". It is his aeroplane reg V5-FIS...great aeroplane, recently resprayed and all new interior...lots of power for a C182...three blader as well. Dont have phone number but you can try the local flying club and get his number from there but dont say it is to rent one otherwise they will phone him and then rent it for you for an additional unwanted costs.
If you cant come right there, there is another C182 V5-JOG that is also for rent..Try and get the info again from the local club but once again do so in different manner to get that info.
If you want a C210 try and get one from Atlantic Aviation in Swakopmund..I think they also rent from time to time depending on your experiece levels.
Hope this give you a better idea of things...
Shout if you need more info...