Hi,
the easiest way to learn what to do about READ ONLY tablespaces and
their files is to ask RBDMS itself.
Mount the database using binary controlfile from April 7 backup. Issue
ALTER DATABASE BACKUP CONTROLFILE TO TRACE;
ORADEBUG SETMYPID
ORADEBUG TRACEFILE_NAME
Check the trace file named in the last command. Carefully check where
the names of READ ONLY tablespace datafiles are placed. Do they appear
in CREATE CONTROLFILE statement? So by now you'll have a working example.
BTW, I've not noticed any UNDO tablespace. Did you just forget about it?
You'll need SYSTEM, SYSAUX and **UNDO** when recreating controfile.