I look forward to hearing how it goes. I’m attempting to get my hoary old D&D group to do a West March saga.
For my own Fallout campaign I’m not going full West March, but I’m using the threat zones from the Powered by Apocalypse 2nd Ed RPG. It requires a lot less up-front work since you, in a gross oversimplification, you just use a clock face with two zones surrounding the center (AKA Players).
Since my Fallout Saga is called “Vault 52 - the Neighbors of Area 51” then New Vegas would be to the south, NCR to the west, etc., with each direction having a near and far zone. I then just write down the basics of what is in those zones.
This is a lot less work than making the GM map, but I do admit a Fallout West-March style saga is easier than in traditional fantasy RPG - you can use real world maps, maps from the various Fallout and Wasteland games, or even the hellscape of Darwin’s World or even Meriga from Gamma World.