I have an Android, multiple Sailfish versions and a UT roms are installed on my device. I can easily boot into any of them. However because the main rom is the Android, I had to figure out how to backup my other roms.
First I thought would use the rom swap function in TWRP. Unfortunately this is not supported in neither v33 and the older version if the second rom is non Android.
Finally I have came up with my own solution: I boot into a Sailfish rom and as root (using tar to keep the symlinks) compress the other roms into a separate file. (The roms are stored in /android/media/0/multiroms/roms folder.)
Then I can transfer the archived roms to a usb stick or PC to store.
If I need to restore any of them, I just "un-tar" with a new name into the mentioned folder and it is ready to boot.
Hopefully I will never have to install/setup Sailfish from scratch if I mess it up again.

Because now I am able to backup and restore my Sailfish roms, I do not need to build a version for myself anymore.