In case there are others going through the frustration I was experiencing....

When trying to install using the latest version of MultiROM (20160417), I would get the following error:

updating partition details...
...done
Full SELinux support is present.
Changing mounts to ROM utouch_stable...
Current boot sector was used as base for fake boot.img!
system-image-upgrader failed
Restoring mounts...
Processing boot.img for Ubuntu Touch
Extracting boot image...
Found dtb
Decompressing ramdisk...
Ramdisk uses GZIP compression
Compressing ramdisk...
Updating partition details...
...done
MTP already enabled
MTP enabled

I used Flashify to manually install an older version of MultiROM (TWRP_multirom_bacon_20160221-01.img) which I downloaded from:
https://www.androidfilehost.com/?w=files&flid=27804

Then, I was able to install the latest stable build without error.