well, after i beat the judjes by the skin of my teeth, the way i leveled up was by:

save

go into the corridor (have gambits set to use heal magic rather than items. 60 or 70 percent health. no lower)

pick up a book and let your guys fight until theyre all wiped out.

change the party to the two (prefrebly strongest) reserve characters.

Leg it back to the save crystal and save.

repeat as nessecery.