Well the Debootstrap Wiki page really helped. Of course I had to add my own utilities, especially the networking ones, to make the system more usable out of the box. I've also added in more files. Maybe I should start a blog or edit the Wiki page to reflect some of the meager changes.
For example, here's a working multistrap.conf to install EmDebian Grip Stable.
bootstrap=Grip Debian Security
aptsources=Grip Debian Security
packages=busybox-static dropbear htop ifupdown iproute iputils-ping mc mtd-utils procps tmux triggerhappy u-boot-tools udev vim-tiny
I tried using vanilla Debian by changing the bootstrap to Grip and the aptsources to Debian and Security, but it wouldn't boot. Maybe I wasn't trying hard enough. That's alright, EmDebian is quite good enough. I like how small it is. I'll keep the backup rootfs, try out some tips from the UBIFS wiki page: