Hello,
 
I had that problem at one time.  My husband worked out of the home.  I used
the fed-ex or ups small shipping boxes.  Constructed them to the size I
needed.  Place it against the back of the area.  Making sure the sticky
part was down under the litter box.  Placing the litter box on top against
it.  But, since then we have made some amends.  Other ideas I would
probably look into is going to hardware store and looking around to see
what catches my eye to help with the situation.  The other thing is maybe
looking at some plastic containers and seeing what may fit in the cage and
adjust it to work.  I call it improvising to the situation to make it work
for you and your ferts.  Keeps everyone mentally stimulated.  :).
 
Hopefully this information may help you.
 
Dooks,
NeeJa and the MOD's (Masters of Disaster)
[Posted in FML issue 3423]