Epson scanner install issues with Silverblue

I am trying to use an Epson scanner with SilverBlue 30. I currently have the scanner driver and scanning apps installed inside a toolbox container, which is clunky but works.

However it seems a better approach would be to use a flatpak’ed app (for example VueScan ) with the Epson scanner drivers installed as an rpm-ostree layered package - or am I getting this wrong?

The Epson iscan drivers have three components (data, core and plug-in). Using rpm-ostree I can install data and core but get the error below for the plug-in, which I am confused by as I thought /var was writeable in SilverBlue.

mkdir: cannot create directory ‘/var/lib/iscan’: Read-only file system
/usr/sbin/iscan-registry: line 155: /var/lib/iscan/interpreter: No such file or directory

Has anyone had experience with this kind of installation?