Hi Bob,
I hope you dont mind my advice as well. I have been to the Victoria falls in September. You will love it and make sure that if you get a chance to swim in the devils pool (at the top of the falls) that you take it - amazing experience.
As for marmite - yep have heard this too, or b vitamin tablets as the mosis hate the yeasty smell.
I opted for insect repelllant with DEET which I applied before dusk and when anywhere near water and also aftersun (I think boots soltan) that has anti mosi in it. I am very juicy and dont remember getting bitten too badly. You can also get pens to apply to the bites to stop the sting.
In terms of anti malarials I took some one a day tablets - I cant remember the name now but they were fab - no sdie effects at all. They are only available on a private prescription and although expensive to know there are no side effects is fab.
I wore long trousers, socks and trainers and just applied repellant to the juicy ankles and any exposed areas.
Are you staying Zambia side or Zimbabwe side?
Hope you have a fantastic time - am very jealous.
If you need any more advice please ask.
Heather