Saving a basemap plot background

I have a rather complex basemap-derived plot that I want to save as animation.
In essence, it uses the blumarble() to add a nice background, plots some
stuff on top of that, and also has an inset with a map of the world that
shows the area of the main map.

The problem is that memory usage as I iterate through the frames that will
eventually make up my animation, rises very fast. I read a post some time ago
on how to store the background, so it didn't have to be recreated everytime

There's an example on how to actually do this for basemaps from J Whitaker,
but I can't get this to work on my example. Ideally, I would like to store
the inset in a function, and my main background in another function, and
restore each axis directly. My attempt follows (which produces a blank image)
is at <>

Many thanks!