I'll try the verbal picture.  Tobin's sounds like mine.  Same place too.
Box is about 6 inches wider than PP.  BTW the brand I have is 
'Adventurer'.  Entire front (from a users perspective, not FIF) is 
held on with hooks and eyes on the inside so I don't have to scrape 
knuckles when loading/unloading PP, it'll slide out.  I can unhook 
the hooks and the entire front comes off.  A small piece 
of wood on the bottom keeps the PP from sliding around.  The hinge 
for the lid is lower than the actual top of the box.  This provides 
the opening to be lower than the rim for comforts sake.  There is 
also enough room to install a TP holder with TP within the lid.  The 
lid is held open with a piece of cord so it doens't crash into the 
cabinets and places the TP in a useable location.  Enough space 
inside for extra TP, chemicals, small fire extinguisher and other 
things.  You MUST use the special RV TP or it won't 
dissolve properly with the proper chemicals.  The valve for dumping 
contents from top to bottom pulls straight out.  I cut an opening in 
the box front for this, remember to round over edges.  To do it right 
one should cover the box with the matching upholstery material.  Mine 
is just plain wood (1/2' plywood BTW)

> I'd love to see a picture of the box.  This would be a HANDY thing to have
> when traveling with two kids!

- Jeff
'80 Westi, '67 Sqbk, '64 Ford Crewcab, '87 Subaru Wagon 4WD
Grass Valley, California