200e

I just want to make sure I understand.

 Is it correct that the 222e can only be properly installed in a 12 or
18 cabinet?

Also since as I understand it, say you have a 6 unit boat, which I
take is more or less the center boat in the 18 unit cabinet. So would
it be practical at a later time to modify say a 6U boat to form an 18
unit cabinet? (or a 4 into a 12?)