We installed a pet flap with magnetic closing ability, into the closure under or bed. Then installed a small muffin fan with a screen to vent it outside. Works really well and "Duke" uses it faithfully. It's easy to get to and always out of sight.
Each time we have guest, the first thing they ask is "where is his litterbox"?
Sorry the pix is so dark, but you will get the idea.
2013 Silverado 2500 HD Duramax/Allison Tuned
Aviator Wright Flyer #1919
"First In, Last Out". 11B4Y
DAV, MOPH, VFW, 5/7 Cav,1/8 Cav Assoc.
11th ABN Pathfinder Co. N7MIP