expdp generates ORA-01555

I'm trying to perform a datapump export on a 3.5TB 11.2.0.2 database.  The export runs for a very long time (>12hours), but then generates an ORA-01555.  The thing is that all of the non-system tablespaces are in read only mode and I'm the only user signed into the database.  The UNDO tablespace is set to autoextend and isn't nearly to the largest size it can grow.  Undo_management=auto and undo_retention=1800. 

Should I try creating a new UNDO tablespace with a very LARGE max size for this event?  And, then drop the tablespace after the export? 

Do you have any other suggestions?