I use boot manager, can boot roms from sdcard.
https://play.google.com/store/apps/details?id=com.drx2.bootmanager.lite
Sent from my DOWNGRADED EVO 3D
Each Rom has its own partitions. The data is not shared. Also need a sdcard with lots of space.
I also use nandroid backup to install Rom, boot manager is old and doesn't work with new installers.
Sent from my DOWNGRADED EVO 3D