Kim, I have the same Midwest cage.  I love everything about it, *except*
that darn channel at the bottom that collects everything.  I could fit
only one large litter pan, that left the other corner open, which my
ferrets delighted in using as the potty spot whenever the mood struck,
even if I placed blankies there.  I recently bought a *secondnature* dog
litter pan.  It is miniature size, 20" X 24" X 5".  It covers the entire
side of the cage they use.  It has a lower front entry, so they can just
back in on the fly.  It won't fit through the door, just lift the cage
from the tray and slide it in place inside the wire.  I use paper instead
of litter as that seems to work better for me, but it is deep enough for
litter.  I found my pan at PetCo, probably other places would have it.
There are smaller/larger sizes available.
 
Ardith
[Posted in FML issue 4687]