PaulS, you hit it pretty close to the head. It is an array, but in this case it won't change. Can it be declared as a constant so that it doesn't take up RAM?
I didn't understand the array, so I was treating it as a long string and trying to cut a substring out of it.
The following code prints the 7 characters with no other manipulation required:
lcd.print(room_text[ (Unit_ID - 1) ]) ;
My other "discovery" is that I don't have to have constant length text phrases--the commas establish the array index.