Howzit fellow African!
So I have done a fair bit of work in your part of the world. I think we need to clear up first by what you mean by accuracy. You can get relative accuracy and absolute accuracy. For relative accuracy, you will be limited to the accuracy of your GPS system. So it you measure 2 points on the ground with your RS and then with a tape measure, the distance will be the same. For this method you dont need any external control system to provide a position for your base. Just suck a single, uncorrected position for your base and away you go.
Absolute accuracy is a bit different in that the system is relative to an established coordinate system like UTM or similar.You survey should then be similar to the one that someone did next door since you are using the same coordinate system and lot a temporary, unfixed one. But if needed and you have to get an absolutly accurate survey, you are in a bit of a jam which is a limitation of a L1 only receiver. You are far to far away for any CORS to work properly. (> than 20km baseline I assume). There are a few control points published, but these are most likely destroyed, or on a local system. There was a private CORs called MozNET but I think its only for Maputo.
Setting up you receiver to collect data for a long period of time doesn’t help anything. You just collect an average of errors that are not corrected anyway. You will still be 2-3m from WGS84 any way.
If you dont need to provide an absolute accurate survey, then dont worry about it. At least use a proper Geoid model for your survey as you will be about 25m off your real height vertically. And place some proper marks on the ground that will last. You never know when you or someone else will want to revisit this survey of yours and will want some information about how you determined your system and how to "calibrate’ to it.
Good luck!