Setting Xen dom0 on an SD card - how?

Greetings - I'd like to set up Alpine Linux as dom0 for a new home server box, an Intel i3 w/ 250 GB SSD. My plan is to have it start up from the SD card, and then later set up the SSD for a couple of domU systems.

I've downloaded the "XEN" 3.5.2 image and copied it to a 4 GB SD card (on Mac). It boots up fine, I can go through the setup-alpine motions, with or without preceding setup-xen-dom0, but then I get stuck, trying to save the config to the suggested /dev/mmblk0 fails (r/o media).

Looks like I'm confused about the installation process. Should I power up via a USB stick, and then save to SD card in the setup-alpine sequence? I guess I'm also sort of in the dark how the XEN image image differs from other downloads.

The two Xen wiki pages don't refer to this Xen download, hence my question: which path to follow, where to look in the docs/forums?

Many thanks for tips to help get me on the right track,
- Jean-Claude Wippler